Introduce support for parsing pretty dialect types, currently with a very

    restricted grammar.  This will make certain common types much easier to read.

    This is part tensorflow/mlir#1 of 2, which allows us to accept the new syntax.  Part 2 will
    change the asmprinter to automatically use it when appropriate, which will
    require updating a bunch of tests.

    This is motivated by the EuroLLVM tutorial and cleaning up the LLVM dialect aesthetics a bit more.

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PiperOrigin-RevId: 242234821