Quick fixes do not provide good support for readonly files

[rcahoon]

Description of issue

The Quick Fix menu in VS Code provides several options to fix common compiler errors, such as creating a missing method in a class.

However, this menu can be misleading for users when the affected files are marked as readonly in VS Code using the files.readonlyInclude workspace setting.

When a file is marked readonly, a Quick Fix option may still be presented to add a method or other class member to it. Selecting that option seems to have a couple of different possible behaviors:

1. If the file is not open in an editor tab, the Quick Fix operation has no effect but presents no message to the user explaining why
2. If the file is open in an editor tab, the Quick Fix operation will seem to apply the requested change, and the language server receives updated content for the file (meaning the red squiggle goes away). However, the updated content is not actually written to disk. Builds will fail with compilation errors. If the editor tab is closed, then the language server will refresh from the file on-disk and the red squiggle will return. Even though the changes are in-memory-only, the file does not show the white circle on the tab header indicating unsaved changes.

Requested change

Change to a more intuitive behavior for the Quick Fix options:

• Hide (or gray out) any Quick Fix options that would require changes to readonly files
• Present a popup message to the user after the Quick Fix is selected explaining that it can't be used on readonly files

At the least, the Quick Fix should not make in-memory-only changes.

Software versions

VS Code: Tested on both 1.96.2 and 1.106.3
Java Extension: 1.50.0
OS: MacOS 15.6.1

[fbricon]

The java language server is not aware of the vscode-specific files.readonlyInclude. We should provide a matching setting to send to the server, and have the server ignore all change requests to such files.

[fbricon]

So Eclipse allows adding a "locked" flag to files or folders. I haven't seen any workspace-wide locking configuration.

VScode glob patterns for inclusions/exclusions is much more powerful/convenient

So translating glob patterns into exact Eclipse lock configuration is gonna be tricky.