ScopeTowerProcessors.kt contains a few code snippets
that look like `collectCandidates(...).filter { ... }.map { ... }`.
Filter argument is always side-effect free, so it is safe
to merge `filter` and `map` calls into one for-loop.
The change also makes sense, because modified functions are quite hot.
For example `NoExplicitReceiverScopeTowerProcessor.simpleProcess`
produces 11,392,768 ArrayList instances (~1.08% of all objects)
when compiling the compiler according to aprof at the moment of writing.
On my machine the change improves compilation speed of the compiler up to 5%.
Alexey Tsvetkov
2ff28ebced