[Debugify] Optimize debugify original mode

[Debugify] Optimize debugify original mode

Before we start addressing the issue with having
a lot of false positives when using debugify in
the original mode, we have made a few patches that
should speed up the execution of the testing
utility Passes.

For example, when testing a large project
(let's say LLVM project itself), we can face
a lot of potential DI issues. Usually, we use
-verify-each-debuginfo-preserve (that is very
similar to -debugify-each) -- it collects
DI metadata before each Pass, and after the Pass
it checks if the Pass preserved the DI metadata.
However, we can speed up this process, since we
don't need to collect DI metadata before each
Pass -- we could use the DI metadata that are
collected after the previous Pass from
the pipeline as an input for the next Pass.

This patch speeds up the utility for ~2x.

Differential Revision: https://reviews.llvm.org/D115622