[lldb] Add SBCompileUnit::GetIsOptimized (#222403)
Expose Module::GetIsOptimized through the SB API so clients can tell
whether a compile unit was built with optimization. This change is
motivated by lldb-dap, where I want to extend the protocol::CompileUnit
with this information.
The new tests build the same source with and without -O1, so the test
case can no longer share a build with the others.
