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

docs/src/configuring-zed.md

@@ -1517,7 +1517,8 @@ To interpret all `.c` files as C++, files called `MyLockFile` as TOML and files
   "show_other_hints": true,
   "show_background": false,
   "edit_debounce_ms": 700,
-  "scroll_debounce_ms": 50
+  "scroll_debounce_ms": 50,
+  "toggle_on_modifiers_press": null
 }
 ```
 
@@ -1539,6 +1540,22 @@ Use the `lsp` section for the server configuration. Examples are provided in the
 Hints are not instantly queried in Zed, two kinds of debounces are used, either may be set to 0 to be disabled.
 Settings-related hint updates are not debounced.
 
+All possible config values for `toggle_on_modifiers_press` are:
+
+```json
+"inlay_hints": {
+  "toggle_on_modifiers_press": {
+    "control": true,
+    "shift": true,
+    "alt": true,
+    "platform": true,
+    "function": true
+  }
+}
+```
+
+Unspecified values have a `false` value, hints won't be toggled if all the modifiers are `false` or not all the modifiers are pressed.
+
 ## Journal
 
 - Description: Configuration for the journal.