Implement spaceMatching config to detect space changes in HTML diffs

[Copilot]

The library was normalizing all whitespace (including   entities), making it impossible to detect when spaces were added or removed from HTML text.

Changes

• Modified AbstractDiff::convertHtmlToListOfWords(): Conditionally preserve non-breaking spaces (\xc2\xa0) when spaceMatching is enabled
• Modified AbstractDiff::normalizeWhitespaceInHtmlSentence(): Skip collapsing multiple consecutive spaces when spaceMatching is enabled (still normalizes newlines)
• Added test fixtures: nbsp-spaces-added.html validates space detection, nbsp-spaces-default-behavior.html validates backward compatibility

Usage

$config = HtmlDiffConfig::create();
$config->setSpaceMatching(true);

$old = '<p>Text&nbsp; &nbsp;</p>';
$new = '<p>Text&nbsp; &nbsp; &nbsp; &nbsp;</p>';

$diff = HtmlDiff::create($old, $new, $config);
// Now detects and highlights the additional spaces

The spaceMatching option defaults to false, preserving existing behavior.

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Original prompt

---

This section details on the original issue you should resolve

<issue_title>Issue with detecting additional/removed spaces in html text</issue_title>
<issue_description>Hello. I noticed that if some additional spaces were added into a text or removed from a text then there is no difference detected. Is it possible to configure HtmlDiff to handle this case? If it's not then maybe it's worth to implement/fix?

Example:

• Old content:

<p>Just a simple text&nbsp; &nbsp;</p>

• New cotent:

<p>Just a simple text&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;</p>

Expected output should show that additional spaces were added.

Thanks for any feedback or tips!</issue_description>

<agent_instructions>New configuration option that doesn't break backwards compatibility</agent_instructions>

Comments on the Issue (you are @copilot in this section)

• Fixes Issue with detecting additional/removed spaces in html text #128

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