[lldb/Interpreter] Make OptionGroupPythonClassWithDict options non-required

When using `OptionGroupPythonClassWithDict` options in an `OptionGroup`
with other `Options`, it can happen that the combinaison of some options
of each group makes the command invalid.

To solve that issue, this patch adds a bitmask argument to the
`OptionGroupPythonClassWithDict` constuctor that is used to mark each
option as required (or not).

If the `required_options` bitmask isn't passed to the constructor, the
class will keep its default behaviour, making the `--script-class` and
`--python-function` required.

rdar://65508855

Differential Revision: https://reviews.llvm.org/D97910



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