Merge changes in distributed vim runtime

[krischik]

There are a few changes in the ada plugin distributed with the vim runtime which need to merged.

It's mostly spelling mistakes and missing &cpo boilerplate code.

However the runtime version has support for gnatxref which needs further investigation. I believe gnatxref hat been superseded and is not a part of the GNAT toolchain any more and support has been removed by @thindil

[thindil]

If I remember correctly, I removed the support for gnatxref mostly because gnatxref works far from perfect. Especially when it was looking for references in third-party packages. And I think it is true now that gnatxref is almost dead. It is still included in GNAT, just probably no longer maintained. Its role is taken now by Language Server Protocol implementation: https://github.com/AdaCore/ada_language_server.

But Vim doesn't have built-in support for LSP, so ALS require a third-party plugin to work. There are several available options, some of them mentioned in ALS README.md file. I use ALE: https://github.com/dense-analysis/ale, as it also has support for gnatpretty.

[TamaMcGlinn]

I'm not sure about Vim, but NeoVim does have built-in support for LSP, and I use that and these two to get excellent language support:

Plug 'TamaMcGlinn/nvim-lspconfig'
Plug 'TamaMcGlinn/nvim-lsp-gpr-selector'

The former is a fork just because Ada-related changes have been rejected for lspconfig because no other users use it, and the latter is my own addition for Alire support and support for multi-gpr projects.