Overhaul indexing mechanisms and algebra in booster

[jberthold]

The indexing mechanism is currently discarding relevant rules when the subject term to rewrite contains function calls in indexed positions. This causes the booster to return stuck where it should instead return aborted.
One instance of this problem was addressed in #4117 but the indexing mechanism should generally be overhauled:

• internalised collections currently get index Anything
• domain values currently get index Anything
• the index should distinguish function symbols from constructors
• when the subject term index is Anything or a function symbol, rewriting must consider all rules.

A more elaborate write-up of the problems and a sketch of a new implementation is in a related gist