[lldb/Plugins] Add support of multiple ScriptedThreads in a ScriptedProcess

This patch adds support of multiple Scripted Threads in a ScriptedProcess.

This is done by fetching the Scripted Threads info dictionary at every
ScriptedProcess::DoUpdateThreadList and iterate over each element to
create a new ScriptedThread using the object instance, if it was not
already available.

This patch also adds the ability to pass a pointer of a script interpreter
object instance to initialize a ScriptedInterface instead of having to call
the script object initializer in the ScriptedInterface constructor.

This is used to instantiate the ScriptedThreadInterface from the
ScriptedThread constructor, to be able to perform call on that script
interpreter object instance.

Finally, the patch also updates the scripted process test to check for
multiple threads.

rdar://84507704

Differential Revision: https://reviews.llvm.org/D117071



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