MCP: allow extra properties for tool calls

[andrew-sol]

Allow passing extra params to MCP tools besides those that the tool was initialized with.

Why?

Because VS Code (unlike other IDEs) caches the MCP tools and does not start MCP servers until they are required by an agent. Because of that, there are situations when MCP tools get updated, but VS Code still uses the old tool params for the first request. In case a param was removed, it still sends it. And I need to test this specific case, I need to handle that param for compatibility purposes.

How does it currently work?

I can add an additional param in the "Parameters Overview" pane, but I get an error must NOT have additional properties upon clicking the "Call Tool" button.