Python bindings: drop MLIREmitter and related functionality

    This completes the transition of Python bindings to use the declarative
    builders infrastructure instead of the now-deprecated EDSC emitter
    infrastructure.  The relevant unit tests have been replicated using the new
    functionality and the remaining end-to-end compilation tests have been updated
    accordingly.  The latter show an improvement in brevity and readability.

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PiperOrigin-RevId: 241713489