vscode-json-languageserver support (#4164)

* vscode-json-languageserver-bin support

VSCode JSON languageserver has schema support for linting and
completions.

I have enabled snippets support (`snippetSupport`) even if it is not
fully supported. `label` that comes with completions response can be
used as well.

* Test fix.

* vscode-json-languageserver instead of vscode-json-languageserver-bin

vscode-json-languageserver is more up-to-date (about 1 year old),
vscode-json-languageserver-bin is 4 years old.

* Use git root.

* Documentation update.

* Trying to sort ordering issue.

* One more attempt

* One more attempt

* Uppercase seems to win.

* Clean-up

* Clean-up 2

* Test removed.

ale_linters/json/vscodejson.vim

@@ -0,0 +1,16 @@
+" Author: Dalius Dobravolskas <dalius.dobravolskas@gmail.com>
+" Description: VSCode json languageserver
+
+function! ale_linters#json#vscodejson#GetProjectRoot(buffer) abort
+    let l:git_path = ale#path#FindNearestDirectory(a:buffer, '.git')
+
+    return !empty(l:git_path) ? fnamemodify(l:git_path, ':h:h') : ''
+endfunction
+
+call ale#linter#Define('json', {
+\   'name': 'vscodejson',
+\   'lsp': 'stdio',
+\   'executable': 'vscode-json-languageserver',
+\   'command': '%e --stdio',
+\   'project_root': function('ale_linters#json#vscodejson#GetProjectRoot'),
+\})