[lldb/test] Update TestScriptedProcess to use skinny corefiles

This patch changes the ScriptedProcess test to use a stack-only skinny
corefile as a backing store.

The corefile is saved as a temporary file at the beginning of the test,
and a second target is created for the ScriptedProcess. To do so, we use
the SBAPI from the ScriptedProcess' python script to interact with the
corefile process.

This patch also makes some small adjustments to the other ScriptedProcess
scripts to resolve some inconsistencies and removes the raw memory dump
that was previously checked in.

Differential Revision: https://reviews.llvm.org/D112047



Signed-off-by: Med Ismail Bennani <medismail.bennani@gmail.com>