Add feature to define LSP settings in g:ycm_language_server

[Felixoid]

In ycm-core/YouCompleteMe#4272, I asked if it's possible to define global LSP settings in .vimrc

Here's the patch that adds this feature, so the settings option will be global with overrides from .ycm_extra_conf.py.

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This change is 

[puremourning]

Thanks for the PR!

I think this is OK and inline with how our built-in completes can set default config, so I'm happy with the general approach, just there's quite a big bug with the implementation doing a shallow copy and only allowing limited layering.

[puremourning]

thanks! just a couple of nits actually.

[puremourning]

@puremourning reviewed 4 files and all commit messages, and made 1 comment.
Reviewable status: 1 of 2 LGTMs obtained (waiting on @Felixoid).

[mergify]

Thanks for sending a PR!

[mergify]

Merge Queue Status

✅ The pull request has been merged at c816c9c

This pull request spent 40 minutes 21 seconds in the queue, including 40 minutes 11 seconds running CI.
The checks were run on draft #1810.

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