Optimize performance of StyleFromMatchedRulesForElement function

During the cross-line text deletion process in the rich text editor,
the StyleFromMatchedRulesForElement function retrieves a list of 
CSS rules for the selected area. The function internally uses the
MergeAndOverrideOnConflict method, which has a time complexity of
O(N^2).

When there are numerous variables on the selected element or its
ancestor elements, the MergeAndOverrideOnConflict function destroy
temporary CSSPropertyName objects.

To address this, unnecessary calls to CSSPropertyValue::Name() have 
been reduced. Furthermore, in the StyleFromMatchedRulesForElement 
function, initialize the style using the first matched_rule to 
reduce the number of merges, thereby decreasing the overall time 
consumption.

Bug: 440387012
Change-Id: Id9c900072c7d31e079bf0a996c92470e22b8ac2a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6874842
Reviewed-by: Peng Zhou <zhoupeng.1996@bytedance.com>
Reviewed-by: Dan Clark <daniec@microsoft.com>
Commit-Queue: Peng Zhou <zhoupeng.1996@bytedance.com>
Auto-Submit: hewro <ihewro@gmail.com>
Cr-Commit-Position: refs/heads/main@{#1506901}

• AUTHORS[diff]
• third_party/blink/renderer/core/css/css_property_value_set.cc[diff]
• third_party/blink/renderer/core/editing/editing_style.cc[diff]