Expand support for multiple extension uris

[jsignell]

Related Issue(s):

• Expand support for multiple extension uris #1084

Description:

From issue:

In #1081 we added support for older schema URIs to the ProjectionExtension. This behavior should be generalized so other extensions can use it easily. Ideas:

• Add get_schema_uris() to the base mixin
• Refactor the base has_extension() to check against get_schema_uris() instead of get_schema_uri()
• Backport any extensions that have older-but-compatible schema uris (thinking maybe label at least?)

This doesn't solve the problem, it's more of a band-aid -- if a newer version of an extension is incompatible with the Python structure, we don't have a mechanism to "migrate".

xref #448 which is our tracking issue for the general problem of extension versions.

I looked over the merged PRs from the last year or so to try to get a sense of which extensions had gotten updates recently.

I also added the previous versions to the prev_extension_ids in the ExtensionHooks. This means that when the item is migrated, the extension schema uri gets updated as well. Note: It looks like there is a mechanism for migrating per-extension. You can see it in LabelExtensionHooks.migrate

PR Checklist:

• pre-commit hooks pass locally
• Tests pass (run scripts/test)
• Documentation has been updated to reflect changes, if applicable
• This PR maintains or improves overall codebase code coverage.
• Changes are added to the CHANGELOG. See the docs for information about adding to the changelog.

[gadomski]

LGTM, just a couple light touchups.