Add a way to toggle inlay hints with modifiers #2 (#25766)

https://github.com/zed-industries/zed/pull/25752 with fixes on top

* Ensures no flickering happens for all modifiers `: false` case
* Dismisses the toggled state on focus out
* Reworks cache state so that "enabled" and "toggled by modifiers" are
different states with their own lifecycle

Release Notes:

- N/A

crates/language/src/language_settings.rs

@@ -9,7 +9,7 @@ use ec4rs::{
     Properties as EditorconfigProperties,
 };
 use globset::{Glob, GlobMatcher, GlobSet, GlobSetBuilder};
-use gpui::App;
+use gpui::{App, Modifiers};
 use itertools::{Either, Itertools};
 use schemars::{
     schema::{InstanceType, ObjectValidation, Schema, SchemaObject, SingleOrVec},
@@ -932,6 +932,13 @@ pub struct InlayHintSettings {
     /// Default: 50
     #[serde(default = "scroll_debounce_ms")]
     pub scroll_debounce_ms: u64,
+    /// Toggles inlay hints (hides or shows) when the user presses the modifiers specified.
+    /// If only a subset of the modifiers specified is pressed, hints are not toggled.
+    /// If no modifiers are specified, this is equivalent to `None`.
+    ///
+    /// Default: None
+    #[serde(default)]
+    pub toggle_on_modifiers_press: Option<Modifiers>,
 }
 
 fn edit_debounce_ms() -> u64 {