[FIRRTL][Dedup] Rework hashing for perf and bug fixes. (#7420)

Primary change is to only generate and populate mappings for
sources of values, and not each value themselves.

Values are identified using these base numberings plus an appropriate
offset.

The main benefit of this is to greatly reduce the number of entries in the
`indices` map.
When handling operations with many block arguments (module-like's with many
ports) or with many results (instances of those module-like's) this greatly
reduces the pressure on the `indices` map.  For these designs, dedup now runs
dramatically faster and uses significantly less memory.

Also separates location of the value impl, such that if a Value's impl is storage
inline into an Operation or Block such that there is aliasing, the two
are given different numbers (and especially the numbering isn't changed).

On a synthetic design containing a module with 2^20 ports and 256 instances of
that module, this is the difference between completing in 20s and OOM'ing on my
machine after running for 30 minutes.

Functional changes:

Fixes #7415.
Fixes #7416.
Also fixes deduping if block arg types are different (but unused).

This is done by hashing block count, and each block's numbering between
as well as the types of its arguments before that block's operations.

Additionally fixes use of numberings (indices) before it was
populated where attribute processing for inner symbol ports
hashed using the block argument's numbering before it was populated.