[Gap Decorations]: Implement Bidirectional rule shorthand

This CL introduces the `rule` shorthand as part of the gap decorations
feature [1]. The `rule` shorthand sets the `column-rule` and `row-rule`
to the same value.

The CL augments `css_parsing_utils::ConsumeGapDecorationsRuleShorthand`
to accept corresponding width, style, and color values for hydration
upon successful parsing. The task of adding the properties has been
moved to the caller, not the consumption function. This approach
simplifies adding properties for bidirectional rules and maintains the
same convention as the Border shorthand.

[1]: https://drafts.csswg.org/css-gaps-1/#propdef-rule

Bug: 357648037
Change-Id: I9ac1993e599236e99f018e458b6e38f2d437668e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6543211
Reviewed-by: Alison Maher <almaher@microsoft.com>
Commit-Queue: Sam Davis Omekara <samomekarajr@microsoft.com>
Reviewed-by: Kevin Babbitt <kbabbitt@microsoft.com>
Cr-Commit-Position: refs/heads/main@{#1464436}