Update to the standard function docs

[TristonianJones]

Provide more useful documentation for the CEL types, functions, and macros

[TristonianJones]

@jnthntatum PTAL

[jnthntatum]

Some optional suggestions for clarifications. otherwise LGTM

[sergiitk]

Thanks for the useful documentation update, @TristonianJones!
One remark: I still found the old table format incredibly convenient as a concise overview of what methods are a part of the standard library. Would you consider bringing back the table at the top of the "Standard Definitions" sections, above the new in-detail docs?