Change escaping from block to escaper in HtmlContent component page

[VladyslavSikailo]

Purpose of this pull request

This pull request replaces deprecated $block->escapeHtml() to $escaper->escapeHtml()

Affected DevDocs pages

• https://devdocs.magento.com/guides/v2.4/ui_comp_guide/components/ui-htmlcontent.html

Links to Magento source code

• https://github.com/magento/magento2/blob/2.4-develop/lib/internal/Magento/Framework/View/Element/AbstractBlock.php#L900

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running tests

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