Use tsserver to drive vue-typescript-plugin (fix Vue file completion)

[Cheaterman]

Everything in the title ; as it currently is, completion in *.vue files is not working - not at all out of the box, and very broken if trying to use modern vue-language-server the same way one used to use volar or vls - I'm not 100% sure but despite it being the same project as volar/vls (or a fork), I suspect it really expects to be driven through tsserver nowadays - this seems to work perfectly without the user even needing to change anything in their .vimrc.

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This change is 

EDIT: I'm sure in an ideal world there would be a fully separate build.py argument for Vue, so that we wouldn't need to "pollute" the tsserver/package.json file with Vue-specific stuff, but I figured it might be overkill and doesn't make a whole lot of difference anyway (~4MB in node_modules).

[puremourning]

how can I test this simply? I don't vue

[puremourning]

I tried the test app in ycm-core/lsp-examples repo and got this:

[Cheaterman]

I think the package.json in the lsp-examples repo needs the very same changes I put here, lemme take a look.

EDIT: So, the snippet.vim seems no longer necessary ; I didn't need to edit anything in the example other than adding the missing tsconfig.json - VLS is now dead in favor of @vue/typescript-plugin, including for non-typescript-enabled codebases ; see my before and after screenshots attached, and the associated PR to the lsp-examples repo here.

Before :

After :

More screenshots with extra usage examples

EDIT2 : Just one more screenshot for good luck :

EDIT3: And in fact a couple more just to demonstrate that it works both with TypeScript enabled and disabled :
Auto-completing with TypeScript disabled (same as above screenshot, except no lang="ts") :

Making an invalid TypeScript call to String.prototype.replace() doesn't show any issues in JS mode :

But obviously TypeScript isn't happy about it :

Thanks for your patience 😁