racket: support racket-langserver lsp (#3808)

* racket: support racket-langserver lsp

* racket-langserver: find highest dir with init.rkt

* autoload/ale/racket: re-indent to 4 spaces

* racket: lint: sort supported tools

* racket: lint: function!

This is _not_ needed anymore, but the lint wants it. See :help E127

* racket-langserver: do not use new dict format

* racket: lint: use snake_case

* add tests for racket-langserver

* racket-langserver tests: correct result values

test/test-files/racket/simple-script/foo.rkt

@@ -0,0 +1,3 @@
+#lang racket/base
+
+(displayln "foo")