feat(ooxml): write the seven text properties onto a run of a docx or pptx

[andiwand]

🤖 Generated with Claude Code

Step 3 of the inline formatting plan (docs/design/document-editing.md, decisions 11, 13 and 14). Rebased onto main after #895 merged.

The cut. A w:t and an a:t share their w:r / a:r with their siblings, so text_set_style cuts the run around the text with TreeEditor::isolate, each part keeping its w:rPr / a:rPr, and writes the delta into the part that holds the text.

docx. CT_RPr is a sequence Word enforces, so each property lands at its rank (run_property_order) and replaces an existing one whole, since a stale w:themeColor would win over a new w:val. w:bCs, w:iCs and w:szCs follow their siblings. A highlight is w:highlight for one of Word's sixteen names and a w:shd w:val="clear" w:fill shading otherwise; only one of the two stays. A test pins the saved w:rPr byte for byte between the w:rFonts and the w:lang the fixture had.

The reader learns w:shd on a run where no highlight names a colour, so a saved shading renders on reopen. Four corpus files carry one, and their reference pages are regenerated and pinned here: sample1 now shows its "inverse video" run white on black where it was white on white; 15KB, 23KB and physics carry white fills on runs, which Word paints too, and move one anti-aliased pixel column at most.

pptx. The toggles and the size are a:rPr attributes, the colour an a:solidFill and the highlight an a:highlight, each at its place in the CT_TextCharacterProperties sequence. A run without an a:rPr gets one ahead of its a:t; a highlight taken away removes the element, since there is no none.

Shared. ooxml_util gains insert_in_sequence, hex_color, highlight_name and points, over the one sixteen-name table read_color_attribute also reads.

Verified. 11 new DocumentEdit tests over inline docx and pptx packages and one reader test for the shading; 443 tests of the document, odf, ooxml and html suites pass; the touched sources are clean under Homebrew clang -Wall -Wextra -Werror. Headless LibreOffice reopens an edited style-various-1.docx and .pptx and reads every property back, the #123456 shading included.