Refactor combo box with browse

[cj-radcliff]

This change removes the deprecated ComboBoxWithBrowse button from the dart plugin. It exchanges it with a standard ComboBox. The functionality has been tested and is confirmed to be identical.

New Component: DartComboBoxWithBrowseButton.java is included in the branch.
EDT Safety: All three major UI areas (Remote Debug Configuration, SDK Settings, and Project Generator) are now using asynchronous, non-blocking ReadActions
for file system operations.
Build: The project compiles successfully with ./gradlew compileJava.
Scope: The changes are strictly limited to the UI refactoring and necessary threading fixes.
Summary of Changes

Core Component: Implemented DartComboBoxWithBrowseButton as a reusable, async-safe UI component.
Remote Debug Editor: Moved project indexing and searching to background threads.
SDK Settings: Refactored SDK validation and version loading to be non-blocking.
Project Generator: Implemented async SDK validation with result caching to satisfy the wizard's synchronous validation requirements without blocking the EDT.
The places to test:

Launch the IDE
Run the following command from the third_party directory:
1 ./gradlew runIde
(Note: Based on the build.gradle.kts, you can also specify a target version, e.g., ./gradlew runIde -Pide=IntelliJ -PideV=2024.2)

Verify the Changes
Once the IDE is running, you can find the modified UI components in these locations:
Dart Remote Debug Configuration (Smart Suggestions)

Open a Dart project or create a new one.
Go to Run -> Edit Configurations...
Click the + button and select Dart Remote Debug.
Look at the Dart project field.
Verification: In the combo-box-reset branch, this should be a ComboBox with a browse icon (folder icon) on the right. It should automatically suggest paths to any folders containing a pubspec.yaml file in your current workspace.
Dart SDK Settings (Centralized Setup)

Go to File -> Settings (or IntelliJ IDEA -> Settings on macOS).
Navigate to Languages & Frameworks -> Dart.
Look at the Dart SDK path field.
Verification: This field should now use the new ExtendableTextField implementation. When you click the browse button or change the path, the version label below it should update automatically using the centralized logic in DartSdkUtil.
New Project Wizard

Go to File -> New -> Project...
Select Dart from the left sidebar.
Check the Dart SDK path field here as well.

[gemini-code-assist]

Code Review

This pull request introduces a custom DartComboBoxWithBrowseButton component and refactors several Dart configuration editors to perform SDK and project path resolution asynchronously using non-blocking read actions. While these changes improve UI responsiveness, several critical threading violations were identified in DartGeneratorPeer where UI components are accessed or updated from background threads. There are also concerns regarding potential memory leaks due to DocumentListener registrations that lack proper disposal, and a minor simplification was suggested for project path handling.

[cj-radcliff]

/gemini

[pq]

This is awesome!

Consider also re-running the baselines so we can see the fruits of your cleanup?

./third_party/tool/update_baselines.sh

[cj-radcliff]

This is awesome!

Consider also re-running the baselines so we can see the fruits of your cleanup?

./third_party/tool/update_baselines.sh

Does the build not update baselines? I didn't know this was a manual process

[pq]

Correct. A script is as automatic as we want it since we want to ensure a thoughtful manual review. (My biggest worry is the baselines creeping out without us realizing it.)

If this creates a lot of friction down the road, I'd be more than happy to discuss alternatives.

Thanks!

[cj-radcliff]

Updated to re-add deleted comments.

[pq]

🎉

Thanks a million for your thoughtful follow-ups!

[pq]

Once the verifier bits are fixed up, LGTM!