Fix React unrecognized-prop warning for style field data attributes

[sneridagh]

Problem

The console showed:

React does not recognize the data-style-blockWidth prop on a DOM element. If you intentionally want it to appear in the DOM as a custom attribute, spell it as lowercase data-style-blockwidth instead.

Cause

toStyleFieldDataAttributes in packages/plate/components/editor/plugins/style-fields-plugin.ts built the attribute as data-style-${fieldName} using the raw field name. For blockWidth that yields data-style-blockWidth. React only forwards data-* attributes whose suffix is lowercase, so it dropped the attribute and warned.

Fix

Kebab-case the field name before building the attribute, so it becomes data-style-block-width — the idiomatic HTML data-attribute form, which also round-trips cleanly via dataset.styleBlockWidth.

• Single-word fields (align, theme) are unchanged, so existing CSS selectors like [data-style-align='left'] keep working.
• The acceptance tests read the --block-width CSS variable, not this attribute, so they are unaffected.
• Updated the affected unit-test expectations in block-width-plugin.test.ts; all 26 tests pass.

Notes

Swept the repo for any consumer of the old camelCase form — none remained.