tree-sitter-mlir: add a more complete grammar

Contribute a grammar, along with associated tests, from the upstream
project maintained at https://github.com/artagnon/tree-sitter-mlir. The
new grammar includes several fixes, and successfully parses 60-80% of
MLIR tests in the Arith, Math, ControlFlow, SCF, Tensor, Affine, and
Linalg dialects.

Differential Revision: https://reviews.llvm.org/D144408