Rollup merge of #125754 - Zalathar:conditions-num, r=lqd

coverage: Rename MC/DC `conditions_num` to `num_conditions`

Updated version of #124571, without the other changes that were split out into #125108 and #125700.

This value represents a quantity of conditions, not an ID, so the new spelling is more appropriate.

Some of the code touched by this PR could perhaps use some other changes, but I would prefer to keep this PR as a simple renaming and avoid scope creep.

`@rustbot` label +A-code-coverage

Author: matthiaskrgr