Refactor KeybindingKeystroke (#37065)

This pull request refactors the `KeybindingKeystroke` struct and related
code to improve platform abstraction. The changes centralize
platform-specific logic within `KeybindingKeystroke` and update its
usage throughout the codebase, making the API more consistent and less
error-prone.



Release Notes:

- N/A

crates/gpui/src/keymap/binding.rs

@@ -57,7 +57,7 @@ impl KeyBinding {
             .split_whitespace()
             .map(|source| {
                 let keystroke = Keystroke::parse(source)?;
-                Ok(KeybindingKeystroke::new(
+                Ok(KeybindingKeystroke::new_with_mapper(
                     keystroke,
                     use_key_equivalents,
                     keyboard_mapper,