Support clojure-dart #615

Support clojure-dart source files.

Currently, clojure-dart files are basically clojure source files that compiles to dart.
See:

• https://github.com/Tensegritics/ClojureDart
• https://github.com/Tensegritics/ClojureDart/blob/816344d4abaf5165fe55ebf3af662af7d3ab3ca8/doc/differences.md

Expected behavior

Clojure-mode should support clojure-dart files (.cljd).

Actual behavior

Current clojure-mode does not detect .cljd files.

Steps to reproduce the problem

Environment & Version information

clojure-mode version

clojure-mode (version 5.14.0)

Emacs version

28.0.91

Operating system

MacOS 12.0.1