Form Block: Default to showing form related blocks when inserting child blocks

### Impacted plugin

Jetpack

### What

When a child block is added in the middle of a form, default blocks are shown such as paragraph and image (before clicking on the browse all button):

Ideally the first block options that appear should be form related, such as text, name, email and consent.

Suggested in internal testing: p8oabR-Ym-p2#comment-6734

### How

As a continuation from this PR - https://github.com/Automattic/jetpack/issues/26889 - perhaps the new Form category can be shown by default.

Start with the Jetpack Form Block child-block inserter and review the continuation work referenced in issue #26889. Reproduce the insertion flow shown in the issue, then verify that form-related choices such as text, name, email, and consent appear before general blocks.

Written by the indexing model from the issue text.