Refactor and fix Config<->Value mechanism (#10896)

# Description
Our config exists both as a `Config` struct for internal consumption and
as a `Value`. The latter is exposed through `$env.config` and can be
both set and read.
Thus we have a complex bug-prone mechanism, that reads a `Value` and
then tries to plug anything where the value is unrepresentable in
`Config` with the correct state from `Config`.

The parsing involves therefore mutation of the `Value` in a nested
`Record` structure. Previously this was wholy done manually, with
indices.
To enable deletion for example, things had to be iterated over from the
back. Also things were indexed in a bunch of places. This was hard to
read and an invitation for bugs.

With #10876 we can now use `Record::retain_mut` to traverse the records,
modify anything that needs fixing, and drop invalid fields.

# Parts:

- Error messages now consistently use the correct spans pointing to the
problematic value and the paths displayed in some messages are also
aligned with the keys used for lookup.
- Reconstruction of values has been fixed for:
	- `table.padding`
	- `buffer_editor`
	- `hooks.command_not_found`
	- `datetime_format` (partial solution)
- Fix validation of `table.padding` input so value is not set (and
underflows `usize` causing `table` to run forever with negative values)
- New proper types for settings. Fully validated enums instead of
strings:
  - `config.edit_mode` -> `EditMode` 
  	- Don't fall back to vi-mode on invalid string
  - `config.table.mode` -> `TableMode`
- there is still a fall back to `rounded` if given an invalid
`TableMode` as argument to the `nu` binary
  - `config.completions.algorithm` -> `CompletionAlgorithm`
  - `config.error_style` -> `ErrorStyle`
    - don't implicitly fall back to `fancy` when given an invalid value.
- This should also shrink the size of `Config` as instead of 4x24 bytes
those fields now need only 4x1 bytes in `Config`
- Completely removed macros relying on the scope of `Value::into_config`
so we can break it up into smaller parts in the future.
- Factored everything into smaller files with the types and helpers for
particular topics.
- `NuCursorShape` now explicitly expresses the `Inherit` setting.
conversion to option only happens at the interface to `reedline`

crates/nu-table/src/common.rs

@@ -1,6 +1,6 @@
 use nu_color_config::{Alignment, StyleComputer, TextStyle};
-use nu_protocol::TrimStrategy;
 use nu_protocol::{Config, FooterMode, ShellError, Span, Value};
+use nu_protocol::{TableMode, TrimStrategy};
 
 use crate::{
     clean_charset, colorize_space_str, string_wrap, NuTableConfig, TableOutput, TableTheme,
@@ -174,24 +174,23 @@ fn is_cfg_trim_keep_words(config: &Config) -> bool {
 }
 
 pub fn load_theme_from_config(config: &Config) -> TableTheme {
-    match config.table_mode.as_str() {
-        "basic" => TableTheme::basic(),
-        "thin" => TableTheme::thin(),
-        "light" => TableTheme::light(),
-        "compact" => TableTheme::compact(),
-        "with_love" => TableTheme::with_love(),
-        "compact_double" => TableTheme::compact_double(),
-        "rounded" => TableTheme::rounded(),
-        "reinforced" => TableTheme::reinforced(),
-        "heavy" => TableTheme::heavy(),
-        "none" => TableTheme::none(),
-        "psql" => TableTheme::psql(),
-        "markdown" => TableTheme::markdown(),
-        "dots" => TableTheme::dots(),
-        "restructured" => TableTheme::restructured(),
-        "ascii_rounded" => TableTheme::ascii_rounded(),
-        "basic_compact" => TableTheme::basic_compact(),
-        _ => TableTheme::rounded(),
+    match config.table_mode {
+        TableMode::Basic => TableTheme::basic(),
+        TableMode::Thin => TableTheme::thin(),
+        TableMode::Light => TableTheme::light(),
+        TableMode::Compact => TableTheme::compact(),
+        TableMode::WithLove => TableTheme::with_love(),
+        TableMode::CompactDouble => TableTheme::compact_double(),
+        TableMode::Rounded => TableTheme::rounded(),
+        TableMode::Reinforced => TableTheme::reinforced(),
+        TableMode::Heavy => TableTheme::heavy(),
+        TableMode::None => TableTheme::none(),
+        TableMode::Psql => TableTheme::psql(),
+        TableMode::Markdown => TableTheme::markdown(),
+        TableMode::Dots => TableTheme::dots(),
+        TableMode::Restructured => TableTheme::restructured(),
+        TableMode::AsciiRounded => TableTheme::ascii_rounded(),
+        TableMode::BasicCompact => TableTheme::basic_compact(),
     }
 }