Implement replacetextEx_char, reimplement Splittext to match new 515 behavior

[MyNameIsRomayne]

Very simple one-liner piggybacking off jointext and spltitext, with an update to Splittext so that it functions properly.

Basically, splittext has been updated in 515 to include the start and end of the string, so the current implementation of Splittext now remembers that and pre/appends those parts to the first/last elements.

The splittext unit tests were updated based off the output from DM for 515:

Originally this was just going to be a one-liner for replacetextEx_char, but after being informed of the changes needed to Splittext I decided to go ahead and do that too, so that this works.