[llvm][utils] Support dereferencing llvm::Optional lldb formatter

Add deref support to `llvm::Optional` in `lldbDataFormatters.py`.

This creates a synthetic provider that adds dereference support, but otherwise proxies all access to the underlying value.

With this change, an optional value can be displayed by running `v *someOptional`, and its contents can be accessed with the arrow `operator->`, for example `v someOpt->HasThing`. This matches expressions usable from expression evaluation.

See also D97165 and D97524.

Differential Revision: https://reviews.llvm.org/D97525