Insert blocks at top of post when post title is selected

[mchowning]

Summary

This PR updates the behavior when inserting a block which the post's title is selected. Previously, the block would be inserted at the bottom of the post, but now it will be inserted at the top of the post. This work is being done in advance of addressing #632 (missing "Add New Block" indicator when inserting a block from the post's title) so that we're inserting the post at the proper location before we add an "Add New Block" indicator for the insertion position.

Related gutenberg PR

Before	After

Testing

Post Title selected scenario

1. Load demo app
2. Tap on the post Title to select it
3. Add any block
4. Observe that the newly added block is inserted at the top of the post

No block selected scenario

1. Load demo app
2. Do NOT select any block
3. Add any block
4. Observe that the newly added block is inserted at the bottom of the post

Any block selected scenario

1. Load demo app
2. Select any block other than the post's Title
3. Add any block
4. Observe that the newly added block is inserted below the previously selected block

Update release notes

• If there are user facing changes, I have added an item to RELEASE-NOTES.txt.

[etoledom]

Thank you for taking care of this @mchowning!
Tested via WordPress/gutenberg#16440 (review)

Since this PR targets v1.10, let's wait until the code freeze is finished to merge this and WordPress/gutenberg#16440

[mchowning]

Since this PR targets v1.10, let's wait until the code freeze is finished to merge this

Hey @etoledom ! Based on the conversation we just had, I'm going to go ahead and merge this for 1.9.