This allows for diagnostics emitted during parsing/verification to be surfaced to the user by the language client, as opposed to just being emitted to the logs like they are now.

Differential Revision: https://reviews.llvm.org/D102293

This provides information when the user hovers over a part of the source .mlir file. This revision adds the following hover behavior:
* Operation:
  - Shows the generic form.
* Operation Result:
  - Shows the parent operation name, result number(s), and type(s).
* Block:
  - Shows the parent operation name, block number, predecessors, and successors.
* Block Argument:
  - Shows the parent operation name, parent block, argument number, and type.

Differential Revision: https://reviews.llvm.org/D101113

This information isn't useful for general compilation, but is useful for building tools that process .mlir files. This class will be used in a followup to start building an LSP language server for MLIR.

Differential Revision: https://reviews.llvm.org/D100438