[mlir][llvm] Use TableGen to import compare ops from LLVM IR.

The revision imports compare operations using TableGen generated
builders, instead of using the special handlers defined by the Importer.
It therefore adds a new llvmArgIndexes field that allows to specify
a mapping between MLIR argument and LLVM IR operand indexes if they do
not match. Additionally, the FCmp op is extended with an additional
builder and all compare operations are extended with verification
traits to ensure the operands types match. These extensions simplify
the logic of the newly introduced builders and are in line with the
compare operations define by the arithmetic dialect.

Reviewed By: ftynse

Differential Revision: https://reviews.llvm.org/D135855