[mlir:vscode] Add support for viewing and editing a bytecode file as .mlir

This commit adds support for interacting with a (valid) bytecode file in the same
way as .mlir. This allows editing, using all of the traditional LSP features, etc. but
still using bytecode as the on-disk serialization format. Loading a bytecode file this
way will fail if the bytecode is invalid, and saving will fail if the edited .mlir is invalid.

Differential Revision: https://reviews.llvm.org/D132970