CMM-2466: Hide the auto-generated Reader excerpt for <br> posts

[nbradbury]

TL;DR

Fixes CMM-2466

In Reader post detail, posts written with Shift+Enter line breaks (<br>) and no manual excerpt showed their whole text twice: once as the grey excerpt under the header, then as the content. This PR makes the auto-excerpt check ignore whitespace so that excerpt is hidden again.

Before and After

Description

Fixes CMM-2466.

• isAutoGeneratedExcerpt hides an excerpt when the stripped post content starts with it.
• WordPress builds the auto-excerpt by stripping tags, which drops <br> with no space (thatthe). HtmlUtils.fastStripHtml turns <br> into a newline, which then became a space (that the), so startsWith failed and the excerpt was treated as author-written.
• Both sides now have all whitespace removed before comparing, instead of collapsing it to single spaces. It can only hide an excerpt that matches the start of the post once whitespace is ignored, and that's the case the check already meant to hide.
• Adds ReaderPostDetailsHeaderViewUiStateBuilderTest (the builder had no tests): an excerpt generated from <br> posts is hidden, and an author-written excerpt is still shown.

The post from the original report now has a manual excerpt (.), so it can't be used to verify the fix. Use a test post instead.

Testing instructions

1. On a WP.com site, set Settings → Reading → "For each post in a feed, include" to Full text. With Excerpt, the Reader API returns the excerpt as the post content and the bug can't reproduce.
2. Create a short post (under 55 words) as a single paragraph with Shift+Enter line breaks, and leave Excerpt empty.
3. Open the post in the Jetpack Reader (pull to refresh first if it was already cached).

• Only the post content is shown, with no grey excerpt under the header. On trunk, the excerpt repeats the post with words run together.

[dangermattic]

	1 Warning
⚠️	PR is not assigned to a milestone.

Generated by 🚫 Danger

[wpmobilebot]

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

	App Name	WordPress Android
	Build Type	Debug
	Version	pr23405-cf87f37
	Build Number	1498
	Application ID	org.wordpress.android.prealpha
	Commit	cf87f37
	Installation URL	1ko2jouaj124g

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

[wpmobilebot]

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

	App Name	Jetpack Android
	Build Type	Debug
	Version	pr23405-cf87f37
	Build Number	1498
	Application ID	com.jetpack.android.prealpha
	Commit	cf87f37
	Installation URL	0275559rkovsg

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

[codecov]

Codecov Report

❌ Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 38.64%. Comparing base (6875444) to head (cf87f37).

Files with missing lines	Patch %	Lines
...views/ReaderPostDetailsHeaderViewUiStateBuilder.kt	0.00%	0 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##            trunk   #23405      +/-   ##
==========================================
+ Coverage   38.62%   38.64%   +0.02%     
==========================================
  Files        2301     2301              
  Lines      128055   128054       -1     
  Branches    18124    18123       -1     
==========================================
+ Hits        49460    49492      +32     
+ Misses      74494    74442      -52     
- Partials     4101     4120      +19     

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[dcalhoun]

Tested well. 🚀