[lldb/Driver] Support terminal resizing
The comment in the Editine.h header made it sound like editline was
just unable to handle terminal resizing. We were not ever telling
editline that the terminal had changed size, which might explain why
it wasn't working.
This patch threads a TerminalSizeChanged() callback through the
IOHandler and invokes it from the SIGWINCH handler in the driver. Our
Editline class already had a TerminalSizeChanged() method which
was invoked only when editline was configured.
This patch also changes Editline to not apply the changes right away
in TerminalSizeChanged(), but instead defer that to the next
character read. During my testing, it happened once that the signal
was received while our ConnectionFileDescriptor::Read was allocating
memory. As el_resize seems to allocate memory too, this crashed.
Reviewers: labath, teemperor
Differential Revision: https://reviews.llvm.org/D79654
(cherry picked from commit d9166ad272847e246799afbb5e0c71874f83aa12)