Make definition lookup mode configurable

[petr-popov]

Summary

This change adds per-server definition_mode to cclsp config.

Supported values:

• symbol (default): existing behavior using symbol_name and optional symbol_kind
• position: direct go-to-definition using line and character

Motivation

The existing name-based find_definition behavior works well for some languages and LLM workflows, but it does not work well for Kotlin/Java go-to-definition from a usage site. In those cases, definition lookup should start
from a concrete cursor position instead of trying to resolve a declaration by name inside the current file.

Changes

• add definition_mode?: "position" | "symbol" to server config
• default to symbol for backward compatibility
• add LSPClient.getDefinitionMode(filePath)
• update find_definition to branch by server definition_mode
• keep existing symbol-based behavior unchanged for default mode
• add tests for both position and symbol modes
• update README with config and usage examples

Validation

• npx tsc --noEmit
• verified Kotlin find_definition from usage positions with definition_mode: "position"