Support remap rules in the segmenter

[eggrobin]

This will vastly improve the maintainability of that copy of the rules, as they can closely mirror the UAX; note that this removes 84 lines from SegmenterDefault.txt, including some nontrivial things like

$NotEastAsian=( $NotEastAsian | [$NotEastAsian - $Spec1_] $X)

or

# LB 10  Treat any remaining combining mark as AL and non-$EastAsian.
$AL=($AL | ^ $CM | (?<=$Spec1_) $CM)
$NotEastAsian=( $NotEastAsian | ^ $CM | (?<=$Spec1_) $CM )

Further, this should make it possible to generate ICU’s old monkeys, which implement the remap rules as specified (only the production implementation integrates them into the regices).

No changes to LineBreakTest.txt except in comments.

[macchiati]

Nice!