Replace the RoseLiteral structure with more program instructions; now,
instead of each literal ID leading to a RoseLiteral, it simply has a
program to run (and a delay rebuild program).
This commit also makes some other improvements:
* CHECK_STATE instruction, for use instead of a sparse iterator over a
single element.
* Elide some checks (CHECK_LIT_EARLY, ANCHORED_DELAY, etc) when not
needed.
* Flatten PUSH_DELAYED behaviour to one instruction per delayed
literal, rather than the mask/index-list approach used before.
* Simple program cache at compile time for deduplication.
