Add support for ink-language-server

This commit add support for ink-language-server, which it does by
largely copying and pasting from the pure-language-server PR that was
merged recently.

The most interesting things to note are:
- ink-language-server is distributed upstream via npm, which is why we
  search through node_modules
- With some coaxing, it can be installed globally - which is why we
  search for a global binary.
- Ink is a funky language, and users will likely need to add
  initialization options.
- I am not incredibly familiar with vimscript; and I may not have done
  some of the buffer searching correctly.

test/command_callback/test_ink_ls_command_callbacks.vader

@@ -0,0 +1,22 @@
+Before:
+  call ale#assert#SetUpLinterTest('ink', 'ls')
+  set ft=ink
+
+After:
+  call ale#assert#TearDownLinterTest()
+
+Execute(should set correct defaults):
+  AssertLinter 'ink-language-server', ale#Escape('ink-language-server') . ' --stdio'
+
+Execute(should set correct LSP values):
+  call ale#test#SetFilename('ink_paths/story/main.ink')
+
+  AssertLSPLanguage 'ink'
+  AssertLSPOptions {}
+  AssertLSPConfig {}
+  AssertLSPProject ale#path#Simplify(g:dir . '/ink_paths/story')
+
+Execute(should accept configuration settings):
+  AssertLSPConfig {}
+  let b:ale_ink_ls_initialization_options = {'ink': {'runThroughMono': v:true}}
+  AssertLSPOptions {'ink': {'runThroughMono': v:true}}