opentelementry-instrumentation-google-genai: add gen_ai.tool.definitions to experimental semconv (#4142)

* opentelementry-instrumentation-google-genai: add gen_ai.tool.definitions to experimental semconv

* Add _to_tool_definition

* Remove unused import

* Add GEN_AI_TOOL_DEFINITIONS to tests.

* Remove uneccesary space.

* address comments: add exclude_none to model_dump and tool type to error message

* address comment: add if/else statement on tool types and add tests for each tool

* dont serilize mcp client sessions in case of synchronous methods

* Refactor _to_tool_definition_common to be more clear

* remove uncessary 'function' key

* fix failing tests: make mcp import conditional

* Update changelog

* Update uv.lock

* address comment: remove undecessary typing.Type

* address comment: make mcp import conditional