Deno: find project root using deno.json/deno.jsonc (#4306)

Deno LSP automatically detects config files named deno.json or
deno.jsonc since version 1.18.

For Deno 1.18+ this means that ALE no longer needs to resolve the
project root. However, removing the project root logic from ALE means
breaking changes for people that are still using an older version.
Adding deno.json to the list of looking files to look for will keep the
behavior consistent and compatible with the Deno config file naming
convention.

See also:
https://deno.com/blog/v1.18#auto-discovery-of-the-config-file

autoload/ale/handlers/deno.vim

@@ -29,6 +29,8 @@ function! ale#handlers#deno#GetProjectRoot(buffer) abort
     endif
 
     let l:possible_project_roots = [
+    \   'deno.json',
+    \   'deno.jsonc',
     \   'tsconfig.json',
     \   '.git',
     \   bufname(a:buffer),