Make return duplication in ControlFlowSimplification less aggressive

[ElektroKill]

Link to issue(s) this covers:
Fixes #2924

Problem

ILSpy was a bit too aggressive when it came to duplicating return blocks which resulted in unoptimal and confusing code with tons of unnecessary return statements which differed from the original source code used to produce the binary. For examples see #2924 (comment) and #2924 (comment).

Solution

• Make the return block duplication step in ControlFlowSimplification less aggressive by effectively making it only perform the duplication if the incoming edge count was 1. This effectively turned it into a simple movement of a block from one container to another.

[dgrunwald]

Can you add a pretty test that demonstrates this improvement?

[siegfriedpammer]

Thank you for the contribution. Sorry for taking so long to get to this!