Add support for jsonnetfmt and jsonnet-lint (#3907)

* update to lates

Signed-off-by: Trevor Whitney <trevorjwhitney@gmail.com>

* fix up docs

Signed-off-by: Trevor Whitney <trevorjwhitney@gmail.com>

* fix docs

Signed-off-by: Trevor Whitney <trevorjwhitney@gmail.com>

* get tests passing

Signed-off-by: Trevor Whitney <trevorjwhitney@gmail.com>

* update regex

Signed-off-by: Trevor Whitney <trevorjwhitney@gmail.com>

* use ale#Pad and AssertFixer

Signed-off-by: Trevor Whitney <trevorjwhitney@gmail.com>

test/fixers/test_jsonnetfmt_fixer_callback.vader

@@ -0,0 +1,38 @@
+Before:
+  Save g:ale_jsonnet_jsonnetfmt_executable
+  Save g:ale_jsonnet_jsonnetfmt_options
+
+  " Use an invalid global executable, so we don't match it.
+  let g:ale_jsonnet_jsonnetfmt_executable = 'xxxinvalid'
+  let g:ale_jsonnet_jsonnetfmt_options = ''
+
+  call ale#test#SetDirectory('/testplugin/test/fixers')
+  call ale#assert#SetUpFixerTest('jsonnet', 'jsonnetfmt')
+
+After:
+  call ale#test#RestoreDirectory()
+  call ale#assert#TearDownFixerTest()
+
+Execute(The jsonnetfmt callback should return the correct default values):
+  call ale#test#SetFilename('../jsonnet_files/testfile.jsonnet')
+
+  AssertFixer {
+  \   'read_temporary_file': 1,
+  \   'command': ale#Escape(g:ale_jsonnet_jsonnetfmt_executable)
+  \     . ' -i'
+  \     . ' %t',
+  \}
+
+Execute(The jsonnetfmt callback should include custom options):
+  let g:ale_jsonnet_jsonnetfmt_options = '--pad-arrays'
+
+  call ale#test#SetFilename('../jsonnet_files/testfile.jsonnet')
+
+  AssertFixer {
+  \   'read_temporary_file': 1,
+  \   'command': ale#Escape(g:ale_jsonnet_jsonnetfmt_executable)
+  \     . ' -i'
+  \     . ' ' . g:ale_jsonnet_jsonnetfmt_options
+  \     . ' %t',
+  \}
+