FEDX-414 Add APIs and update deprecations in preparation for 7.0.0 release

[greglittlefield-wf]

Motivation

react-dart 7.0.0 will contains some breaking changes to APIs that are not yet deprecated in the 6.x line.

The 7.0.0 WIP branch also relies some API additions that aren't present in 6.x, so we'll want to backport them to ensure consumers can transition to these new APIs before setting their lower bounds to 7.0.0.

Solution

• Deprecate APIs to be removed in 7.0.0
• Update existing outdated deprecations for APIs that say they'll be removed in 7.0.0, but won't yet be removed
  • These were mostly Component and its associated APIs, which we don't have a timeline for removing
• Backport APIs htmlMain and useRefInit
• Add draft changelog entry for 7.0.0.
  • I had this written up but not committed anywhere, and figured I'd add it now to help provide context during review of this PR. We can refine this entry later as part of the PRs for the 7.0.0 changes.

QA steps

• Verify CI passes

[aviary3-wk]

Security Insights

No security relevant content was detected by automated scans.

Action Items

• Review PR for security impact; comment "security review required" if needed or unsure

• Verify aviary.yaml coverage of security relevant code

  Questions or Comments? Reach out on Slack: #support-infosec.

[greglittlefield-wf]

@Workiva/release-management-p