Add preferPrimaryDefinition setting for go to definition

[sucicfilip]

Motivation

In apps that reopen classes across many files (packwerk monoliths, engines, etc.), go to definition on a constant always opens a picker listing every file where the class is reopened. Most of the time I just want the file that actually defines the class, and picking it out of the list gets tedious fast.

Implementation

Adds an opt-in featuresConfiguration.definition.preferPrimaryDefinition setting, wired through the existing featuresConfiguration mechanism in GlobalState.

When the setting is enabled and a constant resolves to multiple namespace entries, the definition listener keeps only the entries whose file path matches the fully qualified constant name following the Zeitwerk convention. For example, in this repository RubyIndexer is reopened in over 20 files, but only lib/ruby_indexer/ruby_indexer.rb matches the convention, so that is the single definition returned. If no entry matches the convention, all entries are returned as before. Methods and plain constants are not affected. The filter only applies to classes and modules.

Automated Tests

Added two tests to DefinitionExpectationsTest: one asserting that only the convention-matching file is returned when the setting is on, and one asserting the fallback to all entries when no file matches.

Manual Tests

1. Point the VS Code extension at this branch (e.g. "rubyLsp.bundleGemfile" or a path: entry in your project's Gemfile)
2. Add "rubyLsp.featuresConfiguration": { "definition": { "preferPrimaryDefinition": true } } to your settings and restart the Ruby LSP
3. Open this repository and trigger go to definition on a RubyIndexer reference (it is reopened in over 20 files under lib/). You should land directly in lib/ruby_indexer/ruby_indexer.rb instead of getting a picker
4. Disable the setting and repeat. You should get the usual picker with every definition