The "Step Out" action continues execution until the current function
returns.
Also, LibDebug/StackFrameUtils was introduced to eliminate the
duplication of stack frame inspection logic between the "Step Out"
action and the BacktraceModel.
Previously, we did source-level singlestepping by inserting a
breakpoint at every source line and continued execution until we hit
a breakpoint. We did this because we used to not generate source
locations debug info for library code, and it allowed us to not single
step through lots of library code to get to the next source line
(which is super slow).
Since we now do generate source locations debug info for libraries
(-g1), we can improve the way we implement source level stepping by
stepping at the assembly level until we reach a different source code
location.
