[clang-format] Add the possibility to align assignments spanning empty lines or comments

Currently, empty lines and comments break alignment of assignments on consecutive
lines. This makes the AlignConsecutiveAssignments option an enum that allows controlling
whether empty lines or empty lines and comments should be ignored when aligning
assignments.

Reviewed By: MyDeveloperDay, HazardyKnusperkeks, tinloaf

Differential Revision: https://reviews.llvm.org/D93986