lsp: Make vim support more explicit, add code completions

[V-FEXrt]

• Adds explicit instructions on how to build/install the LSP as a standalone binary
• Adds explicit instructions on how to install/configure the LSP and syntax file in neovim
• Adds support for code completion such that typing % will prompt all PIdents in the current file and typing any other alphanumeric will prompt all opcodes filtered by a fuzzy match
• Updates the hover (and code completion) doc text for an opcode to have more information (ex: opcode class & opcode operands)

Things that should probably be improved

• Instructions for building/installing on neovim are linux specific right now
• Code completion will suggest opcodes in places that don't make sense like the operands

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

[V-FEXrt]

utils/vscode/src/schema/schema.go and utils/vscode/spirv.json being generated and checked it makes this PR look way larger than it actually is. Might not be a bad idea to git ignore those files at some point. I can also just revert them to their last state if that is preferred