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
5c84195b8c