Allow add-ons to register and execute commands

[pvcresin]

Motivation

Ruby LSP add-ons can contribute Code Lenses and other editor features, but there is currently no generic way for an add-on to register and handle the commands referenced by those features. This forces add-ons that need server-side command handling to provide additional editor integration.

Implementation

• Add Addon#commands and Addon#execute_command hooks.
• Register add-on commands through the standard client/registerCapability request after add-ons are loaded.
• Handle the standard workspace/executeCommand request and route it to the add-on that owns the command.
• Respect the client's workspace.executeCommand.dynamicRegistration capability and ignore errored add-ons.
• Document the API and add protocol/server coverage.

Add-ons are loaded after the initialize response, so dynamic registration keeps the existing add-on lifecycle unchanged. The VS Code extension does not require changes because its existing vscode-languageclient dependency handles standard dynamic execute-command registration.

Automated Tests

• test/requests/execute_command_test.rb
• test/global_state_test.rb
• Related Server, Addon, and Code Lens tests
• RuboCop
• Sorbet

Manual Tests

Not run in a full VS Code session. The new server tests verify the dynamic registration payload and command dispatch. An end-to-end test can be performed with an add-on that returns a command from commands, implements execute_command, and exposes a Code Lens using that command.

[pvcresin]

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