Refactor ImportForm as function component and use hooks

[amustaque97]

This PR is a part of issue #22890

Description

Refactor ImportForm as function componenet. All componenet test case are passing.
After changes, it is working as expected.

How has this been tested?

1. Open link http://localhost:8888/wp-admin/edit.php?post_type=wp_block
2. Create a new file with name hello-world.json and paste the below code

{
  "__file": "wp_block",
  "title": "HelloWorld",
  "content": "<!-- wp:heading -->\n<h2 id=\"hello-world-importform\">Hello, World - ImportForm</h2>\n<!-- /wp:heading -->"
}

3. On the reusable blocks page, import the saved file hello-world.json
4. Verify the success message.
5. Upload non-json file and verify an error message.

Screenshots

• In case of invalid file

• In case of a successful import

Types of changes

Code Quality

Checklist:

• My code is tested.
• My code follows the WordPress code style.
• My code follows the accessibility standards.
• I've tested my changes with keyboard and screen readers.
• My code has proper inline documentation.
• I've included developer documentation if appropriate.
• I've updated all React Native files affected by any refactorings/renamings in this PR (please manually search all *.native.js files for terms that need renaming or removal).

[youknowriad]

LGTM 👍 Thanks for the contribution.