Add an anagram helper

[rentalcustard]

When solving crosswords on paper, there's often a space nearby on the page for playing with anagrams, for example by placing all the letters in a ring to make different arrangements easier to see. Since computer solvers don't have this ability at their fingertips, some crossword interfaces provide an anagram helper. A great example can be seen in the Guardian's crossword webapp. To view it:

1. Visit a crossword, e.g. https://www.theguardian.com/crosswords/cryptic/27763#1-across
2. Optionally, put some but not all letters into the solution
3. Click 'anagram helper'
4. Type the letters that should be shuffled
5. Click shuffle

Notice how the letters are now arranged in a ring above, and a possible arrangement is placed into a representation of the space for the solution. Also notice how already-filled letters never move, and you are not allowed to type more letters than there is space for.

Arguably, some of these features make anagramming easier than on pen and paper. I'd say a minimal feature set would be to be able to hit a key combination, type some letters, and see them arranged in a ring.