Keep a paragraph’s closing whitespace on its last row and in its width

[francois-unity]

Keeps the whitespace that ends a paragraph on its last row, and counts it in the paragraph’s block width when it fits, so a block ending in a space neither grows an empty row nor loses its space.

Why: Parley’s line breaker hangs a space that overflows a row and then breaks, so a space that ends the paragraph leaves an empty row behind, and that row counts in the layout height. A block’s max-content width comes from Layout::width(), which leaves trailing whitespace out, so laying the text out again at exactly that width always wraps it. In the native Unity Hub, div().child("Can’t find the version you’re looking for? Visit our ") laid out at 303×40 instead of 303×20 (Inter 13px on a 20px line), and a baseline-aligned row of such fragments dropped its link a line (HUB-8048).

• First commit: when the last rows hold only whitespace after a soft break, parley_paragraph_layout breaks the paragraph again, the earlier rows as before and the last one with no width limit, still aligned within the wrap width. That also removes the empty row Parley leaves after an oversized inline box that ends a paragraph. A forced break (U+2028) still starts its own row.
• Second commit: hanging alone kept the row but not the space, so in a sentence built from fragments the link sat flush against “our”. A block’s width now counts the whitespace that ends its paragraph when it fits in the width the paragraph was given, as a text element’s width (LineLayout::width) already does. When it doesn’t fit, it hangs and stops counting.

How to test

• cargo +1.98.1 test -p gpui_ce_parley: four new tests in text_system/tests/inline_reflow.rs, each failing without the fix: the Hub’s footer sentence as a baseline-aligned flex row (one row, space kept), the closing-space width rule, the text system at its own width with and without a line clamp, and an oversized trailing inline box. block_line_clamp_ignores_wrapped_trailing_whitespace stays green.
• cargo +1.98.1 test -p gpui_ce_elements -p gpui_ce_macos stays green.
• clippy, msrv, test-linux and test-windows stop on the base’s bindgen build-script error before reaching this code; Declare gpui_media’s bindgen build dependency on every host #6 fixes that.
• Unity Hub pins the same two commits on top of unity/wayland-early-app-id (unity/HUB-8048-hub-pin-3, 6f7e4cfe3b), since its pin also carries elements/div: add an aria_url passthrough #4 and the test text system commit.