Added phpstan linter for php. (#772)

* Added phpstan linter for php.

test/test_phpstan_executable_detection.vader

@@ -0,0 +1,113 @@
+Before:
+  Save g:ale_php_phpstan_executable
+  Save g:ale_php_phpstan_level
+
+  let g:ale_php_phpstan_executable = 'phpstan_test'
+
+  call ale#test#SetDirectory('/testplugin/test')
+
+  runtime ale_linters/php/phpstan.vim
+
+After:
+  Restore
+
+  call ale#test#RestoreDirectory()
+  call ale#linter#Reset()
+
+Execute(project with level set to 3):
+  call ale#test#SetFilename('phpstan-test-files/foo/test.php')
+  let g:ale_php_phpstan_level = 3
+
+  AssertEqual
+  \ 'phpstan_test analyze -l3 --errorFormat raw %s',
+  \ ale_linters#php#phpstan#GetCommand(bufnr(''))
+
+Execute(project with default level):
+  call ale#test#SetFilename('phpstan-test-files/foo/test.php')
+
+  AssertEqual
+  \ 'phpstan_test analyze -l4 --errorFormat raw %s',
+  \ ale_linters#php#phpstan#GetCommand(bufnr(''))
+
+Execute(parse output without errors):
+  call ale#test#SetFilename('phpstan-test-files/foo/test.php')
+
+  AssertEqual
+  \ [],
+  \ ale_linters#php#phpstan#Handle(bufnr(''), [" 1/1 [▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓] 100%"])
+
+Execute(parse output with one error):
+  call ale#test#SetFilename('phpstan-test-files/foo/test.php')
+
+  AssertEqual
+  \ [
+  \   {
+  \     'lnum': 9,
+  \     'text': 'Access to an undefined property Test::$var.',
+  \     'type': 'W'
+  \   }
+  \ ],
+  \ ale_linters#php#phpstan#Handle(bufnr(''), [
+  \   ' 1/1 [▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓] 100%',
+  \   'phpstan-test-files/foo/test.php:9:Access to an undefined property Test::$var.',
+  \])
+
+Execute(parse output with three errors):
+  call ale#test#SetFilename('phpstan-test-files/foo/test.php')
+
+  AssertEqual
+  \ [
+  \   {
+  \     'lnum': 9,
+  \     'text': 'Call to method format() on an unknown class DateTimeImutable.',
+  \     'type': 'W'
+  \   },
+  \   {
+  \     'lnum': 16,
+  \     'text': 'Sample message.',
+  \     'type': 'W'
+  \   },
+  \   {
+  \     'lnum': 192,
+  \     'text': 'Invalid command testCommand.',
+  \     'type': 'W'
+  \   }
+  \ ],
+  \ ale_linters#php#phpstan#Handle(bufnr(''), [
+  \   ' 1/1 [▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓] 100%',
+  \   'phpstan-test-files/foo/test.php:9:Call to method format() on an unknown class DateTimeImutable.',
+  \   'phpstan-test-files/foo/test.php:16:Sample message.',
+  \   'phpstan-test-files/foo/test.php:192:Invalid command testCommand.',
+  \])
+
+Execute(parse output for windows filesystem):
+  call ale#test#SetFilename('phpstan-test-files/foo/test.php')
+
+  AssertEqual
+  \ [
+  \   {
+  \     'lnum': 9,
+  \     'text': 'Access to an undefined property Test::$var.',
+  \     'type': 'W'
+  \   }
+  \ ],
+  \ ale_linters#php#phpstan#Handle(bufnr(''), [
+  \   ' 1/1 [▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓] 100%',
+  \   'D:\phpstan-test-files\foo\test.php:9:Access to an undefined property Test::$var.',
+  \])
+
+Execute(parse output for not php file):
+  call ale#test#SetFilename('phpstan-test-files/test.inc')
+
+  AssertEqual
+  \ [
+  \   {
+  \     'lnum': 9,
+  \     'text': 'Access to an undefined property Test::$var.',
+  \     'type': 'W'
+  \   }
+  \ ],
+  \ ale_linters#php#phpstan#Handle(bufnr(''), [
+  \   ' 1/1 [▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓] 100%',
+  \   '/phpstan-test-files/foo/test.inc:9:Access to an undefined property Test::$var.',
+  \])