Name the Value conversion functions more clearly (#11851)

# Description
This PR renames the conversion functions on `Value` to be more consistent.
It follows the Rust [API guidelines](https://rust-lang.github.io/api-guidelines/naming.html#ad-hoc-conversions-follow-as_-to_-into_-conventions-c-conv) for ad-hoc conversions.
The conversion functions on `Value` now come in a few forms:
- `coerce_{type}` takes a `&Value` and attempts to convert the value to
`type` (e.g., `i64` are converted to `f64`). This is the old behavior of
some of the `as_{type}` functions -- these functions have simply been
renamed to better reflect what they do.
- The new `as_{type}` functions take a `&Value` and returns an `Ok`
result only if the value is of `type` (no conversion is attempted). The
returned value will be borrowed if `type` is non-`Copy`, otherwise an
owned value is returned.
- `into_{type}` exists for non-`Copy` types, but otherwise does not
attempt conversion just like `as_type`. It takes an owned `Value` and
always returns an owned result.
- `coerce_into_{type}` has the same relationship with `coerce_{type}` as
`into_{type}` does with `as_{type}`.
- `to_{kind}_string`: conversion to different string formats (debug,
abbreviated, etc.). Only two of the old string conversion functions were
removed, the rest have been renamed only.
- `to_{type}`: other conversion functions. Currently, only `to_path`
exists. (And `to_string` through `Display`.)

This table summaries the above:
| Form | Cost | Input Ownership | Output Ownership | Converts `Value`
case/`type` |
| ---------------------------- | ----- | --------------- |
---------------- | -------- |
| `as_{type}` | Cheap | Borrowed | Borrowed/Owned | No |
| `into_{type}` | Cheap | Owned | Owned | No |
| `coerce_{type}` | Cheap | Borrowed | Borrowed/Owned | Yes |
| `coerce_into_{type}` | Cheap | Owned | Owned | Yes |
| `to_{kind}_string` | Expensive | Borrowed | Owned | Yes |
| `to_{type}` | Expensive | Borrowed | Owned | Yes |

# User-Facing Changes
Breaking API change for `Value` in `nu-protocol` which is exposed as
part of the plugin API.

crates/nu-cli/src/commands/commandline.rs

@@ -70,11 +70,12 @@ impl Command for Commandline {
         _input: PipelineData,
     ) -> Result<PipelineData, ShellError> {
         if let Some(cmd) = call.opt::<Value>(engine_state, stack, 0)? {
+            let span = cmd.span();
+            let cmd = cmd.coerce_into_string()?;
             let mut repl = engine_state.repl_state.lock().expect("repl state mutex");
 
             if call.has_flag(engine_state, stack, "cursor")? {
-                let cmd_str = cmd.as_string()?;
-                match cmd_str.parse::<i64>() {
+                match cmd.parse::<i64>() {
                     Ok(n) => {
                         repl.cursor_pos = if n <= 0 {
                             0usize
@@ -90,22 +91,19 @@ impl Command for Commandline {
                         return Err(ShellError::CantConvert {
                             to_type: "int".to_string(),
                             from_type: "string".to_string(),
-                            span: cmd.span(),
-                            help: Some(format!(
-                                r#"string "{cmd_str}" does not represent a valid int"#
-                            )),
+                            span,
+                            help: Some(format!(r#"string "{cmd}" does not represent a valid int"#)),
                         })
                     }
                 }
             } else if call.has_flag(engine_state, stack, "append")? {
-                repl.buffer.push_str(&cmd.as_string()?);
+                repl.buffer.push_str(&cmd);
             } else if call.has_flag(engine_state, stack, "insert")? {
-                let cmd_str = cmd.as_string()?;
                 let cursor_pos = repl.cursor_pos;
-                repl.buffer.insert_str(cursor_pos, &cmd_str);
-                repl.cursor_pos += cmd_str.len();
+                repl.buffer.insert_str(cursor_pos, &cmd);
+                repl.cursor_pos += cmd.len();
             } else {
-                repl.buffer = cmd.as_string()?;
+                repl.buffer = cmd;
                 repl.cursor_pos = repl.buffer.len();
             }
             Ok(Value::nothing(call.head).into_pipeline_data())

crates/nu-cli/src/commands/keybindings_listen.rs

@@ -112,7 +112,7 @@ pub fn print_events(engine_state: &EngineState) -> Result<Value, ShellError> {
         let o = match v {
             Value::Record { val, .. } => val
                 .iter()
-                .map(|(x, y)| format!("{}: {}", x, y.into_string("", config)))
+                .map(|(x, y)| format!("{}: {}", x, y.to_expanded_string("", config)))
                 .collect::<Vec<String>>()
                 .join(", "),