[clang][dataflow] Use NoopLattice in optional model

Followup to D128352. This patch pulls the `NoopLattice` class out from the `NoopAnalysis.h` test file into its own `NoopLattice.h` source file, and uses it to replace usage of `SourceLocationsLattice` in `UncheckedOptionalAccessModel`.

Reviewed By: ymandel, sgatev, gribozavr2, xazax.hun

Differential Revision: https://reviews.llvm.org/D128356