release: Blueprint 6.7.2

[robmaceachern]

Summary

• Moves the unreleased BlueprintView reentrant-update fix from Main into the 6.7.2 release section.
• Updates the [main] and [6.7.2] changelog comparison links.

Release notes

• BlueprintView now defers view hierarchy updates that are triggered while an update is already in progress, instead of crashing with a "Reentrant updates are not supported" precondition failure. Reentrant invalidations are coalesced and applied on a following main run loop turn.

Validation

• git diff --check

Post-merge

• Draft and publish the GitHub release for 6.7.2 from https://github.com/square/Blueprint/releases using the changelog entry above.