Prior to rB99a7c917eab7, Shift + D was used to set detail size for both
constant and relative detail. The commit added an improved operator for
doing this for constant detail, but left the user without a shortcut to
do this for relative detail.

Interestingly rB99a7c917eab7 only changed this for the Blender keymap,
the Industy Compatible keymap still has the "old" entry.

This patch changes both keymaps to have both entries.

For user experience, the real change here is to have both operators
available on one 'primary' shortcut (Shift+D), the improved
'dyntopo_detail_size_edit' operator will now act on all possible cases.
If it deals with constant detail, it acts as before, if it deals with
relative detail etc, it will call the "old" 'set_detail_size' internally
instead. I assume this adresses what was stated in rB99a7c917eab7:
"Deciding if both detail sizes can be unified needs a separate
discussion"

Also, move dyntopo_detail_size_edit to sculpt_detail.c

Fixes T83828