Add a way to clear parent category

[0nko]

Implements #11427.

After fixing a parent category crash, I realized there's no way to clear the parent category once it's been set. This PR adds a button to do that.

Screen_recording_20240501_182608.webm

To test:

1. Make sure you already have a category hierarchy with some categories having a parent
2. Go to Products -> Tap on a product -> Tap on Categories
3. Tap on a category with a parent category
4. Tap on the Clear parent category button
5. Notice the parent category is removed and the button is disabled
6. Tap on Save
7. Notice the changed category is not in the top level

[wpmobilebot]

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

	App Name	WooCommerce Android
	Flavor	Jalapeno
	Build Type	Debug
	Commit	894493c
	Direct Download	woocommerce-prototype-build-pr11428-894493c.apk

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 40.84%. Comparing base (15144b2) to head (894493c).
Report is 134 commits behind head on trunk.

Files	Patch %	Lines
...products/categories/AddProductCategoryViewModel.kt	0.00%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##              trunk   #11428      +/-   ##
============================================
- Coverage     40.84%   40.84%   -0.01%     
  Complexity     5215     5215              
============================================
  Files          1070     1070              
  Lines         62771    62773       +2     
  Branches       8571     8571              
============================================
  Hits          25639    25639              
- Misses        34825    34827       +2     
  Partials       2307     2307              

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[hichamboushaba]

Nice work @0nko, works well

[hichamboushaba]

very minor np, we could shorten this with something like:

            binding.productCategoryParent.setHtmlText(parentCategoryName.orEmpty())

[0nko]

Oh yeah, good call 👍

[dangermattic]

	1 Warning
⚠️	This PR is assigned to the milestone 18.6. 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.

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