[Custom Fields] Delete fields

[hichamboushaba]

Closes: #14156

Description

This PR adds support for deleting custom fields, it has the following changes:

• Updates the logic of combining custom fields list with pending changes to handle deleted fields.
• Adds logic for handling the delete button in the editor screen, and return the result to the list screen.
• Adds logic to show a notice when a field is deleted.

Steps to reproduce

1. Open an order or product details in the app.
2. Tap on custom fields button or row.
3. Open an existing custom field.
4. Tap on the menu overflow button.
5. Tap on Delete button.

Testing information

• Confirm that deletion works.
• Test the undo behavior.
• Test deleting a newly added field (not saved on the server yet)

Screenshots

Simulator.Screen.Recording.-.iPhone.15.-.2024-10-21.at.17.32.21.mp4

---

• I have considered if this change warrants user-facing release notes and have added them to RELEASE-NOTES.txt if necessary.

Reviewer (or Author, in the case of optional code reviews):

Please make sure these conditions are met before approving the PR, or request changes if the PR needs improvement:

• The PR is small and has a clear, single focus, or a valid explanation is provided in the description. If needed, please request to split it into smaller PRs.
• Ensure Adequate Unit Test Coverage: The changes are reasonably covered by unit tests or an explanation is provided in the PR description.
• Manual Testing: The author listed all the tests they ran, including smoke tests when needed (e.g., for refactorings). The reviewer confirmed that the PR works as expected on all devices (phone/tablet) and no regressions are added.

[dangermattic]

	2 Warnings
⚠️	View files have been modified, but no screenshot or video is included in the pull request. Consider adding some for clarity.
⚠️	This PR is assigned to the milestone 20.9. This milestone is due in less than 2 days. Please make sure to get it merged by then or assign it to a milestone with a later deadline.

Generated by 🚫 Danger

[wpmobilebot]

📲 You can test the changes from this Pull Request in WooCommerce iOS by scanning the QR code below to install the corresponding build.

	App Name	WooCommerce iOS
	Build Number	pr14177-588572d
	Version	20.8
	Bundle ID	com.automattic.alpha.woocommerce
	Commit	588572d
	App Center Build	WooCommerce - Prototype Builds #11282

Automatticians: You can use our internal self-serve MC tool to give yourself access to App Center if needed.

[itsmeichigo]

I tested with both new and existing fields and the deletion and undo work as expected ✅.

I left some non-blocking comments and suggestions below.