OpenDocument/ODT writer: use predefined styles.

[jgm]

Previously the OpenDocument writer emitted a fresh automatic style (L1..Ln, P1..Pn, T1..Tn) for nearly every list, list-item paragraph, block quote, preformatted block, and inline text style. This produced large ODT files, made --reference-doc customization ineffective (the user's predefined styles were never referenced), and gave each list its own indentation independent of any containing block quote.

This commit teaches the writer to reference the predefined styles that LibreOffice ships and that pandoc's reference.odt now exports:

• Bullet lists use List_20_1; ordered lists with default start and decimal format use Numbering_20_1. Non-default ordered lists generate a single named override style (Pandoc_Numbering_N) memoised by (ListNumberStyle, ListNumberDelim); a non-default start value with the default format is expressed via text:start-value on the text:list element instead of a new style.
• List-item paragraphs use List_20_Bullet[_Tight] and List_20_Number[_Tight]. The Tight variants are pandoc-specific (zero top/bottom margin) and are injected into the user's reference.odt if missing, just like the Skylighting token styles.
• Block quotes use the predefined Quotations paragraph style directly. Nested block quotes use a single automatic style that inherits from Quotations and only adds extra margin-left, so a list inside a block quote now inherits its container's indent (ODF output Blockquotes should not have a non-style indent applied #2747).
• Preformatted blocks use Preformatted_20_Text directly.
• Emphasis, Strong, Strikeout, Subscript, Superscript and Code spans use the predefined Emphasis, Strong_20_Emphasis, Strikeout, Subscript, Superscript and Source_20_Text text styles.
• paraStyle/paraStyleFromParent no longer emit a wrapper automatic style when its only attribute would be parent-style-name; the parent name is returned directly.

Closes #9136.
Closes #5086.
Closes #2747.
Closes #3426.
Closes #7336.

Co-authored by: Claude Opus 4.7.