[debugserver] Fix logic to extract app bundle from file path

Fix the logic to find the app bundle in a path by correctly accounting
for paths containing multiple occurrences of `.app`. The new logic will
correctly extract `com.app.Foo.app` from `com.app.Foo.app/com.app.Foo`.

rdar://74666208

Differential revision: https://reviews.llvm.org/D97441