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-table/src/common.rs

@@ -47,7 +47,7 @@ pub fn nu_value_to_string_colored(val: &Value, cfg: &Config, style: &StyleComput
 
 pub fn nu_value_to_string(val: &Value, cfg: &Config, style: &StyleComputer) -> NuText {
     let float_precision = cfg.float_precision as usize;
-    let text = val.into_abbreviated_string(cfg);
+    let text = val.to_abbreviated_string(cfg);
     make_styled_string(style, text, Some(val), float_precision)
 }
 
@@ -99,7 +99,7 @@ pub fn get_value_style(value: &Value, config: &Config, style_computer: &StyleCom
             style_computer.style_primitive(value),
         ),
         _ => (
-            value.into_abbreviated_string(config),
+            value.to_abbreviated_string(config),
             style_computer.style_primitive(value),
         ),
     }

crates/nu-table/src/types/expanded.rs

@@ -118,7 +118,7 @@ fn expanded_table_list(input: &[Value], cfg: Cfg<'_>) -> TableResult {
                 .as_record()
                 .ok()
                 .and_then(|val| val.get(INDEX_COLUMN_NAME))
-                .map(|value| value.into_string("", cfg.opts.config))
+                .map(|value| value.to_expanded_string("", cfg.opts.config))
                 .unwrap_or_else(|| index.to_string());
 
             let row = row + with_header as usize;

crates/nu-table/src/types/general.rs

@@ -207,7 +207,7 @@ fn get_table_row_index(item: &Value, config: &Config, row: usize, offset: usize)
     match item {
         Value::Record { val, .. } => val
             .get(INDEX_COLUMN_NAME)
-            .map(|value| value.into_string("", config))
+            .map(|value| value.to_expanded_string("", config))
             .unwrap_or_else(|| (row + offset).to_string()),
         _ => (row + offset).to_string(),
     }

crates/nu-table/src/unstructured_table.rs

@@ -100,7 +100,7 @@ fn convert_nu_value_to_table_value(value: Value, config: &Config) -> TableValue
             }
         }
         value => {
-            let mut text = value.into_abbreviated_string(config);
+            let mut text = value.to_abbreviated_string(config);
             if string_width(&text) > 50 {
                 text = string_wrap(&text, 30, false);
             }