fix(prettier-plugin-liquid): preserve U+00A0 and don't drop borrowed closing tags

[BJvdA]

What are you adding in this PR?

Fix a @shopify/prettier-plugin-liquid bug where formatting an HTML text node containing only a non-breaking space (U+00A0) inside borrowed-closing-tag contexts produced broken output:

Input:

<p><strong><em>\u00A0</em></strong></p>

Previous output (incorrect — both the NBSP and the </em> are lost):

<p>
  <strong><em></strong>
</p>

Expected output (preserves the NBSP and the </em>):

<p>
  <strong><em> </em></strong>
</p>

Root cause

printTextNode short-circuited whitespace-only text with return ''. Two problems:

1. JavaScript's \s matches U+00A0, but in HTML a non-breaking space is a meaningful character and must not be collapsed away.
2. The early return '' skipped printOpeningTagPrefix / printClosingTagSuffix, which is exactly where tag markers borrowed from the parent (see needsToBorrowParentClosingTagStartMarker) are emitted. When that runs on a whitespace-only text node, the borrowed </em> marker gets silently dropped.

Fix (packages/prettier-plugin-liquid/src/printer/printer-liquid-html.ts)

• Use the HTML whitespace set [ \t\n\r\f] instead of \s for the short-circuit, the trim, and the word split — so U+00A0 (and other non-collapsible Unicode "whitespace") flows through as a regular character.
• When the text really is pure HTML whitespace, still emit printOpeningTagPrefix / printClosingTagSuffix so any borrowed open/close markers survive.

Adds a regression case to the unit-paragraphs printer fixture covering <p><strong><em>\u00A0</em></strong></p>.

What's next? Any followup issues?

None.

What did you learn?

\s in JavaScript matches U+00A0 — which is fine for "is this byte whitespace-ish", but wrong any time you actually care about HTML semantics, where NBSP is non-collapsible content. Whenever a printer special-cases "whitespace-only" nodes, the early-return path also has to honor whatever work the surrounding tag-borrowing logic relies on.

Tophatting

• I added screenshots of the changes (before and after the changes if applicable)

Repro / verification:

yarn workspace @shopify/prettier-plugin-liquid test

The new fixture under unit-paragraphs (it should preserve non-breaking spaces (U+00A0) as text and not drop borrowed closing tags) covers the regression.

Before you deploy

• I included a patch bump changeset (.changeset/preserve-nbsp-html-text.md)