Command Palette: Use WP_HTML_Processor and WP_HTML_Decoder to generate menu label and menu URL

[t-hamano]

Trac ticket:

• https://core.trac.wordpress.org/ticket/64177
• https://core.trac.wordpress.org/ticket/64196

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[t-hamano]

I'll prepare the commit message now, ready for when I commit this pull request.

Command Palette: Use WP_HTML_Processor and WP_HTML_Decoder for menu labels and URLs.

Replace regex-based HTML tag removal with WP_HTML_Processor to properly extract text nodes from menu labels. This ensures only root-level text nodes are
collected.

Additionally, replace html_entity_decode() with WP_HTML_Decoder::decode_attribute() for URL decoding to use the modern HTML API for consistent attribute decoding.

Follow-up to [61124], [61126], [61127], [61142].

Props: wildworks, dmsnell, madhavishah01.
Fixes #64177, #64196.

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Props wildworks, mukesh27.

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