[Speculation] Add Enable signal to Speculator and other small fixes

[asleix]

This PR addresses several issues regarding the speculation implementation:

• Add the $enable control signal of type NoneType to SpeculatorOp, which is responsible for enabling the Speculator.
• Add automatic connection of the enable signal to the edge from a predecessor BB carrying the control signal of NoneType.
• Improve the commit-control routing, where the specTag after a branch isn't merged, but rather forked from the input.
• Fix the tests for speculation passes to include the new enable signal and adapting to the new naming system.
• Fix a bug in CFG.cpp:getBBPredecessorArcs where not initializing BBEndpoints could lead to unexpected errors.

[murphe67]

Looks good from my end, thanks Aleix!