Add new symbol graph generation option for include/skip inherited docs

[cmcgee1024]

Summary

There is a new symbol graph generation option from SwiftPM that controls whether inherited
docs should be included/skipped. Adopt this new option in the DocC plugin.

Dependencies

This PR depends on a 6.3 toolchain that has the SwiftPM changes in it.

Testing

Reviewers can (eventually) use a nightly toolchain with the SwiftPM changes in it
and run one of the command plugins here to specify whether inherited docs should
be skipped or included.

Alternatively, a tester can use any older toolchain and get a warning if the option
is used since SwiftPM has no API for that in older versions.

Checklist

Make sure you check off the following items. If they cannot be completed, provide a reason.

• Added tests
• Ran the ./bin/test script and it succeeded
• Updated documentation if necessary

[cmcgee1024]

@swift-ci please test

[cmcgee1024]

@swift-ci please test