[llvm] [NFC] Add missing bitcode documentation to BitCodeFormat.rst (PR #102555)

[Chris Apple via llvm-commits]

cjappl wrote:

Possibly cc @SLTozer for review, as it seems like you may have done the last batch update of this?

It would be great if there was some unit tests for this in the future, I think this will be a recurring problem. 


There are also some (seemingly crufty) files that define emacs/vim/vscode for llvm IR that are very much out of date, I didn't even bother digging into those.  All of these attributes I added to the docs here are missing in these files, and many more attributes beyond that.

```
llvm/utils/vscode/llvm/syntaxes/ll.tmLanguage.yaml
llvm/utils/emacs/llvm-mode.el
llvm/utils/llvm.grm
llvm/utils/vim/syntax/llvm.vim
```

https://github.com/llvm/llvm-project/pull/102555