[lldb][NFCI] Remove CommandObjectProcessHandle::VerifyCommandOptionValue (#79901)

I was refactoring something else but ran into this function. It was
somewhat confusing to read through and understand, but it boils down to
two steps:
- First we try `OptionArgParser::ToBoolean`. If that works, then we're
good to go.
- Second, we try `llvm::to_integer` to see if it's an integer. If it
parses to 0 or 1, we're good.
- Failing either of the steps above means we cannot parse it into a
bool.

Instead of having an integer out param and a bool return value, the
interface is better served with an optional<bool> -- Either it parses
into true or false, or you get back nothing (nullopt).