[clang-format] Stop alignment sequences on open braces and parens when

aligning assignments.

This was done correctly when aligning the declarations, but not when
aligning assignments.

FIXME: The code between assignments and declarations alignment is
roughly duplicated and
would benefit from factorization.

Bug 25090: https://llvm.org/bugs/show_bug.cgi?id=25090

Patch by Beren Minor. Thank you.

llvm-svn: 249552