Update config directly at assignment (#13332)

# Description

Allows `Stack` to have a modified local `Config`, which is updated
immediately when `$env.config` is assigned to. This means that even
within a script, commands that come after `$env.config` changes will
always see those changes in `Stack::get_config()`.

Also fixed a lot of cases where `engine_state.get_config()` was used
even when `Stack` was available.

Closes #13324.

# User-Facing Changes
- Config changes apply immediately after the assignment is executed,
rather than whenever config is read by a command that needs it.
- Potentially slower performance when executing a lot of lines that
change `$env.config` one after another. Recommended to get `$env.config`
into a `mut` variable first and do modifications, then assign it back.
- Much faster performance when executing a script that made
modifications to `$env.config`, as the changes are only parsed once.

# Tests + Formatting
All passing.

# After Submitting
- [ ] release notes

crates/nu-color-config/src/style_computer.rs

@@ -1,6 +1,6 @@
 use crate::{color_record_to_nustyle, lookup_ansi_color_style, text_style::Alignment, TextStyle};
 use nu_ansi_term::{Color, Style};
-use nu_engine::{env::get_config, ClosureEvalOnce};
+use nu_engine::ClosureEvalOnce;
 use nu_protocol::{
     cli_error::CliError,
     engine::{Closure, EngineState, Stack, StateWorkingSet},
@@ -114,7 +114,7 @@ impl<'a> StyleComputer<'a> {
 
     // The main constructor.
     pub fn from_config(engine_state: &'a EngineState, stack: &'a Stack) -> StyleComputer<'a> {
-        let config = get_config(engine_state, stack);
+        let config = stack.get_config(engine_state);
 
         // Create the hashmap
         #[rustfmt::skip]