Fix share extension dropping text shared alongside images

[joshheald]

Fixes CMM-2397

Description

Sharing a note that contains both text and images into WordPress or Jetpack produced a draft or post with only the images. The text was lost.

Reproduced with Apple Notes and Day One.

Cause.
Text extractors are an ordered list, and the first one to claim the content wins.

URLExtractor is before PlainTextExtractor, and claims anything with a public.url. It doesn't actually handle the images, which are handled later by ImageExtractor, but it does claim all the content. It just doesn't display it

ImageExtractor ran separately, which is why the images still arrived.

Fix. URLExtractor now skips attachments that are images, leaving them to ImageExtractor so the other text extractors after it still run.

Fixing the text loss exposed three further problems in the draft that gets built, also fixed here:

• Images were placed above the text. insertImageAttachment inserted at richTextView.selectedRange, and setHTML leaves the caret at position 0, so every image went to the start of the document. They now append at the end. This is just a judgement call, to be honest, but made sense to me.
• A shared note became a blockquote. combinedContentHTML wrapped selectedText in <blockquote> unconditionally. That suits a passage quoted from a web page, where it pairs with a "Read on " attribution — Safari's JS preprocessing sets selectedText and url together, and that case is unchanged. Text arriving without a source URL is more likely the author's own writing, so it now stays as ordinary paragraphs.
• Paragraph breaks were lost. Shared text arrives as one flat string. Blank lines now become paragraph breaks and single line breaks become <br>.

Note on interleaving

Images shared with text in this way cannot be placed back between the paragraphs they came from. Day One sends the entry as one flat public.plain-text blob; the images carry no name and no position.

Apps that share a TextBundle keep their images inline via the existing handleTextBundle path (added in #11223), which is unaffected by this change.

Testing instructions

Requires a WordPress.com account signed in to the app, since the share extension reads its token from the shared keychain.

The reported bug

1. In Apple Notes or Day One, write a note with a paragraph of text and one or more images.
2. Share → WordPress (or Jetpack) → Post as draft.
3. Open the draft. Expected: the text is in the body and the image(s) is attached below it. On trunk the text is missing.

Paragraphs and quoting
4. Share a note with several paragraphs separated by blank lines. Expected: the paragraph breaks survive, and the text is not wrapped in a quote block.
5. In Safari, select a passage of text on a page and share it. Expected: unchanged from trunk — a blockquote with a "Read on " attribution at the end.

Regression check on packaged notes
6. From a markdown editor that shares a TextBundle (Bear, iA Writer), share a note with text between two images. Expected: unchanged from trunk — images stay in their original positions between the paragraphs.

Share.extension.text.and.images.mp4

Release notes

Added to RELEASE-NOTES.txt.

[dangermattic]

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	Configuration	Release-Alpha
	Build Number	34350
	Version	PR #25987
	Bundle ID	org.wordpress.alpha
	Commit	3c83f21
	Installation URL	5afa12undovlg

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

	App Name	Jetpack
	Configuration	Release-Alpha
	Build Number	34350
	Version	PR #25987
	Bundle ID	com.jetpack.alpha
	Commit	3c83f21
	Installation URL	1mtgii2spmq98

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