Change elements literal parsing to not rely on shaped type being a vector or...

Change elements literal parsing to not rely on shaped type being a vector or tensor.

    This is in preparation for making MemRef a ShapedType. In general, a shaped type should be anything with shape, rank, and element type properties, so use sites shouldn't assume more than that.

    I also pulled the trailing comma parsing out the parseElementsLiteralType (new name) method. It seems weird to have the method parse the type + a trailing comma, even if all call sites currently need that. It's surprising behavior without looking at the implementation.

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PiperOrigin-RevId: 250558363