Avoid duplicated character classes in rx

For example, (any digit digit) should produce "[[:digit:]]",
not "[[:digit:][:digit:]]".

* lisp/emacs-lisp/rx.el (rx--translate-any): Deduplicate character classes.
* test/lisp/emacs-lisp/rx-tests.el (rx-any): Add test case.
1 job for master in 65 minutes and 18 seconds (queued for 1 second)
Status Job ID Name Coverage
  Test
failed #4413
test-all

01:05:18

 
Name Stage Failure
failed
test-all Test
make[2]: *** [check-doit] Error 1
Makefile:319: recipe for target 'check-doit' failed
make[2]: Leaving directory '/builds/emacs/emacs/test'
Makefile:294: recipe for target 'check-expensive' failed
make[1]: *** [check-expensive] Error 2
make[1]: Leaving directory '/builds/emacs/emacs/test'
Makefile:959: recipe for target 'check-expensive' failed
make: *** [check-expensive] Error 2
ERROR: Job failed: exit code 1