regex: Fix some tricky fold problems

regex: Fix some tricky fold problems

As described in the comments, this changes the design of handling the
Unicode tricky fold characters to not generate a node for each possible
sequence but to get them to work within EXACTFish nodes.

The previous design(s) all used a node to handle these, which suffers
from the downfall that it precludes legitimate matches that would cross
the node boundary.

The new design is described in the comments.