Add preconditions to `TestBase.expect()` that catch semantically invalid calls
that happen to succeed anyway. This also fixes the broken callsites caught by
these checks.
This prevents the following incorrect calls:
1. `self.expect("lldb command", "some substr")`
2. `self.expect("lldb command", "assert message", "some substr")`
Differential Revision: https://reviews.llvm.org/D88792
This patch is similar in spirit to https://reviews.llvm.org/D84480,
but does the maccatalyst/macosx disambiguation. I also took the
opportunity to factor out the gdb-remote packet log scanning used by
several testcases into lldbutil functions.
rdar://problem/66059257
Differential Revision: https://reviews.llvm.org/D84576