feat(lsp): add definition and references methods to LSPManager

[amondnet]

Summary

Adds essential LSP code navigation features to LSPManager: definition() and references() methods. These enable IDEs and editors to provide "Go to Definition" and "Find All References" functionality.

Changes

• definition(): Navigate to where a symbol is defined (LSP textDocument/definition request)
• references(): Find all references to a symbol (LSP textDocument/references request)
• Implements LSP 3.17 specification compliance
• Supports multiple response formats:
  • Location
  • Location[]
  • LocationLink[] (with origin information)
• Includes type guards for runtime type checking
• Normalizes location responses for consistent API

Implementation Details

Both methods:

• Accept file path, line, and character position parameters
• Query all available LSP clients for the file
• Handle different response types through type normalization
• Return normalized Location[] format for consistent consumption
• Include error handling and graceful degradation

Test Plan

• New methods added to LSPManager class
• Methods follow LSP 3.17 specification
• Response format handling verified (Location, Location[], LocationLink[])
• Type definitions added for response schemas
• Exported from public API

Related Issues

Closes #13