Metadata Schema

[kenodegard]

Instead of having a highly decentralized process of validating the contents and format of the metadata this introduces a schema that is used to validate/standardize the metadata prior to storage/usage.

Using this schema obsoletes the need to check whether a section is an OPTIONALLY_ITERABLE_FIELDS and other optional styles of defining the metadata (e.g. "build/run_exports" which can be a simple list which implicitly means those values are "weak", or a dict explicitly specifying "weak", "strong", etc. values).

This further helps to centralize the checking of the metadata to where it happens all at once upon parsing the metafile and not randomly throughout the build process and at least theoretically should help users to more easily catch metadata issues.

I'm leaving the cleanup process of removing obsolete code to future PRs.

[mingwandroid]

Thank you for your work again @njalerikson. I look forward to reviewing it as soon as I get some time.

[github-actions]

Hi there, thank you for your contribution!

This pull request has been automatically marked as stale because it has not had recent activity. It will be closed automatically if no further activity occurs.

If you would like this pull request to remain open please:

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Thanks!

[github-actions]

Hi there, thank you for your contribution!

This pull request has been automatically marked as stale because it has not had recent activity. It will be closed automatically if no further activity occurs.

If you would like this pull request to remain open please:

1. Rebase and verify the changes still work
2. Leave a comment with the current status

NOTE: If this pull request was closed prematurely, please leave a comment.

Thanks!