Move most of the peculiar argument handling for external calls into the parser (#13089)

# Description

We've had a lot of different issues and PRs related to arg handling with
externals since the rewrite of `run-external` in #12921:

- #12950
- #12955
- #13000
- #13001
- #13021
- #13027
- #13028
- #13073

Many of these are caused by the argument handling of external calls and
`run-external` being very special and involving the parser handing
quoted strings over to `run-external` so that it knows whether to expand
tildes and globs and so on. This is really unusual and also makes it
harder to use `run-external`, and also harder to understand it (and
probably is part of the reason why it was rewritten in the first place).

This PR moves a lot more of that work over to the parser, so that by the
time `run-external` gets it, it's dealing with much more normal Nushell
values. In particular:

- Unquoted strings are handled as globs with no expand
- The unescaped-but-quoted handling of strings was removed, and the
parser constructs normal looking strings instead, removing internal
quotes so that `run-external` doesn't have to do it
- Bare word interpolation is now supported and expansion is done in this
case
- Expressions typed as `Glob` containing `Expr::StringInterpolation` now
produce `Value::Glob` instead, with the quoted status from the expr
passed through so we know if it was a bare word
- Bare word interpolation for values typed as `glob` now possible, but
not implemented
- Because expansion is now triggered by `Value::Glob(_, false)` instead
of looking at the expr, externals now support glob types

# User-Facing Changes

- Bare word interpolation works for external command options, and
otherwise embedded in other strings:
  ```nushell
  ^echo --foo=(2 + 2) # prints --foo=4
  ^echo -foo=$"(2 + 2)" # prints -foo=4
  ^echo foo="(2 + 2)" # prints (no interpolation!) foo=(2 + 2)
  ^echo foo,(2 + 2),bar # prints foo,4,bar
  ```

- Bare word interpolation expands for external command head/args:
  ```nushell
  let name = "exa"
  ~/.cargo/bin/($name) # this works, and expands the tilde
  ^$"~/.cargo/bin/($name)" # this doesn't expand the tilde
  ^echo ~/($name)/* # this glob is expanded
  ^echo $"~/($name)/*" # this isn't expanded
  ```

- Ndots are now supported for the head of an external command
(`^.../foo` works)

- Glob values are now supported for head/args of an external command,
and expanded appropriately:
  ```nushell
  ^("~/.cargo/bin/exa" | into glob) # the tilde is expanded
  ^echo ("*.txt" | into glob) # this glob is expanded
  ```

- `run-external` now works more like any other command, without
expecting a special call convention
  for its args:
  ```nushell
  run-external echo "'foo'"
  # before PR: 'foo'
  # after PR:  foo
  run-external echo "*.txt"
  # before PR: (glob is expanded)
  # after PR:  *.txt
  ```

# Tests + Formatting
Lots of tests added and cleaned up. Some tests that weren't active on
Windows changed to use `nu --testbin cococo` so that they can work.
Added a test for Linux only to make sure tilde expansion of commands
works, because changing `HOME` there causes `~` to reliably change.

- 🟢 `toolkit fmt`
- 🟢 `toolkit clippy`
- 🟢 `toolkit test`
- 🟢 `toolkit test stdlib`

# After Submitting
- [ ] release notes: make sure to mention the new syntaxes that are
supported

crates/nu-parser/src/flatten.rs

@@ -26,6 +26,7 @@ pub enum FlatShape {
     Flag,
     Float,
     Garbage,
+    GlobInterpolation,
     GlobPattern,
     Int,
     InternalCall(DeclId),
@@ -67,6 +68,7 @@ impl FlatShape {
             FlatShape::Flag => "shape_flag",
             FlatShape::Float => "shape_float",
             FlatShape::Garbage => "shape_garbage",
+            FlatShape::GlobInterpolation => "shape_glob_interpolation",
             FlatShape::GlobPattern => "shape_globpattern",
             FlatShape::Int => "shape_int",
             FlatShape::InternalCall(_) => "shape_internalcall",
@@ -277,7 +279,7 @@ fn flatten_expression_into(
             output[arg_start..].sort();
         }
         Expr::ExternalCall(head, args) => {
-            if let Expr::String(..) = &head.expr {
+            if let Expr::String(..) | Expr::GlobPattern(..) = &head.expr {
                 output.push((head.span, FlatShape::External));
             } else {
                 flatten_expression_into(working_set, head, output);
@@ -286,7 +288,7 @@ fn flatten_expression_into(
             for arg in args.as_ref() {
                 match arg {
                     ExternalArgument::Regular(expr) => {
-                        if let Expr::String(..) = &expr.expr {
+                        if let Expr::String(..) | Expr::GlobPattern(..) = &expr.expr {
                             output.push((expr.span, FlatShape::ExternalArg));
                         } else {
                             flatten_expression_into(working_set, expr, output);
@@ -431,6 +433,25 @@ fn flatten_expression_into(
             }
             output.extend(flattened);
         }
+        Expr::GlobInterpolation(exprs, quoted) => {
+            let mut flattened = vec![];
+            for expr in exprs {
+                flatten_expression_into(working_set, expr, &mut flattened);
+            }
+
+            if *quoted {
+                // If we aren't a bare word interpolation, also highlight the outer quotes
+                output.push((
+                    Span::new(expr.span.start, expr.span.start + 2),
+                    FlatShape::GlobInterpolation,
+                ));
+                flattened.push((
+                    Span::new(expr.span.end - 1, expr.span.end),
+                    FlatShape::GlobInterpolation,
+                ));
+            }
+            output.extend(flattened);
+        }
         Expr::Record(list) => {
             let outer_span = expr.span;
             let mut last_end = outer_span.start;