Add workspace clean command to delete classpath cache

[juchanei]

Changes

• Added new command kotlin.clean.workspace that allows users to clean the Kotlin laguage server workspace
  • This command serves as a recovery mechanism when the classpath cache becomes corrupted, often as a result of local environment inconsistencies (e.g., issues in Gradle configuration), allowing users to reset to a clean state.
• Implements a confirmation dialog to prevent accidental workspace cleaning
• Removes workspace directory and reloads window to apply changes

Testing

• Tested manual cleaning through command palette
• Verified workspace directory is properly removed
• Confirmed window reload behavior works as expected