[Android] inform the host app when an Image Block is deleted

[mzorz]

Describe the bug When an Image block contains an image and the image upload fails for whatever reason, the host app typically keeps track of that somehow to allow the user to retry an upload and to let Gutenberg know which Image Blocks have a failed image within (so the editor knows and is able to correspondingly show the upload error UI to the user). Currently, tapping on the block's trash icon (to remove a failed image) is not informed to the host app, so the app can't update its state to know which images should be retried. This leads to UX communication artifacts, for example the host app's upload error and progress notifications being inconsistent with what can be seen in the editor.

To Reproduce Steps to reproduce the behavior:

0. use WPAndroid (preferably on a clean installation to avoid potentially confusing other media failed issues):
1. Create a new draft on the Block editor
2. turn airplane mode ON
3. add an image block and assign an image to it
4. add another image block and assign another image to it
5. now remove once of the blocks by tapping on the block's trash icon
6. tap on the image on the other block, to get the "retry/remove/retry all" dialog
7. tap on "retry all"
8. Observe the error notification will still say "2 files not uploaded", when in reality we only wanted to upload 1 image, not 2 (as we removed one of the blocks).

Expected behavior When removing an Image Block that contains a failed to upload image, then retrying other failed uploads, count in the notifications should be consistent.

Smartphone (please complete the following information):

• Device: [Pixel emulator]
• OS: [8.0]
• Version [1.17, c6d095edb0f302d07e0e9976831635e918bb1bdd]

Additional context First spotted while testing this https://github.com/wordpress-mobile/WordPress-Android/pull/10791#discussion_r347904111 , and related to the work done in #715, and https://github.com/WordPress/gutenberg/pull/14391/files#diff-a61b3f346c11f42236eb2b1a783bf9bfR93.

Potential solution:

1. on the Gutenberg side, the detection of an image block being removed is already made here. We should also let the callback know not only when an in progress upload is happening (i.e. remove the check for this.state.isUploadInProgress), but also for any other case (and let the host app decide what to do there).
2. on the host app side and specifically the WPAndroid app should remove the mediaId from mFailedMediaIds array in GutenbergEditorFragment, and also call the fragment listener's onMediaDeleted when the user taps on the trash icon on an ImageBlock (pretty much follow the retry Dialog's REMOVE action onClick body ). Otherwise, artifacts in upload progress notification count and upload error notifications may happen, as these rely on what that array contains.

[hypest]

Verified still happening as of WPAndroid v15.0-rc-3.

[jhnstn]

Verified still happening

• WPAndroid v19.2 rc-3