Add buf linter and fixer (#4128)

* Add buf lint to linters

* Add buf format to fixers

* Fix test/linter/test_buf_lint.vader

* Fix test/fixers/test_buf_format_fixer_callback.vader

* Simplify test/test-files/proto/testfile.proto

* Add buf-lint alias and rename linter

ale_linters/proto/buf_lint.vim

@@ -0,0 +1,23 @@
+" Author: Alex McKinney <alexmckinney01@gmail.com>
+" Description: Run buf lint.
+
+call ale#Set('proto_buf_lint_executable', 'buf')
+call ale#Set('proto_buf_lint_config', '')
+
+function! ale_linters#proto#buf_lint#GetCommand(buffer) abort
+    let l:config = ale#Var(a:buffer, 'proto_buf_lint_config')
+
+    return '%e lint'
+    \ . (!empty(l:config) ? ' --config=' . ale#Escape(l:config) : '')
+    \ . ' %s#include_package_files=true'
+endfunction
+
+call ale#linter#Define('proto', {
+\   'name': 'buf_lint',
+\   'aliases': ['buf-lint'],
+\   'lint_file': 1,
+\   'output_stream': 'stdout',
+\   'executable': {b -> ale#Var(b, 'proto_buf_lint_executable')},
+\   'command': function('ale_linters#proto#buf_lint#GetCommand'),
+\   'callback': 'ale#handlers#unix#HandleAsError',
+\})