Allow arguments for the last flag in short flag batch (#8808)

# Description
_Fixes #5923_

Currently `nushell` doesn't allow short flag batches to contain
arguments, despite this being a common pattern in commands like `git
commit -am 'My commit message'`. This PR relaxes this so that the last
flag in the batch can take an argument.

# User-Facing Changes
- `nu::parser::short_flag_arg_cant_take_arg` has been replaced by
`nu::parser::only_last_flag_in_batch_can_take_arg` and is displayed when
a flag other then the last in a short flag batch takes an argument.

# Tests + Formatting
- Both
[`test_parser.rs`](48af0ebc3c/crates/nu-parser/tests/test_parser.rs (L640-L704))
and
[`test_known_external.rs`](48af0ebc3c/src/tests/test_known_external.rs (L42-L61))
have been updated to test the new allowed and disallowed scenarios.

---------

Co-authored-by: sholderbach <sholderbach@users.noreply.github.com>

crates/nu-protocol/src/parse_error.rs

@@ -292,9 +292,9 @@ pub enum ParseError {
     #[diagnostic(code(nu::parser::missing_flag_param))]
     MissingFlagParam(String, #[label = "flag missing {0} argument"] Span),
 
-    #[error("Batches of short flags can't take arguments.")]
-    #[diagnostic(code(nu::parser::short_flag_arg_cant_take_arg))]
-    ShortFlagBatchCantTakeArg(#[label = "short flag batches can't take args"] Span),
+    #[error("Only the last flag in a short flag batch can take an argument.")]
+    #[diagnostic(code(nu::parser::only_last_flag_in_batch_can_take_arg))]
+    OnlyLastFlagInBatchCanTakeArg(#[label = "only the last flag can take args"] Span),
 
     #[error("Missing required positional argument.")]
     #[diagnostic(code(nu::parser::missing_positional), help("Usage: {2}"))]
@@ -473,7 +473,7 @@ impl ParseError {
             ParseError::RequiredAfterOptional(_, s) => *s,
             ParseError::UnknownType(s) => *s,
             ParseError::MissingFlagParam(_, s) => *s,
-            ParseError::ShortFlagBatchCantTakeArg(s) => *s,
+            ParseError::OnlyLastFlagInBatchCanTakeArg(s) => *s,
             ParseError::MissingPositional(_, s, _) => *s,
             ParseError::KeywordMissingArgument(_, _, s) => *s,
             ParseError::MissingType(s) => *s,