Consider shorthands when removing equivalent properties from styles

As part of some editing operations, like removing line-breaks, a DOM
node may get merged into a different inline-block, hence inserted in a
different parent. This operation normally wants the node's original
inline style to be preserved, but we want to avoid redundant properties
based on the inheritance from its new parent.

The RemoveRedundantStylesAndKeepStyleSpanInline method implemented in
the ReplaceSelectionCommand class takes care of the logic to analyze how
the new inheritance affects to the node's style. For inline styles, it
basically uses the RemoveStyleFromRulesAndContext method from the
EditingStyle class.

The root cause of the bug comes from the GetPropertiesNotIn() method and
how it chooses the properties to remove from the CSSPropertyValueSet
instance. The current implementation just iterates along the registered
longhand properties, comparing their values with the respective
properties in the new node's parent. However, this logic doesn't
consider whether the properties' value come from a shorthand declaration
in the original style.

The bug is only reproducible when inspecting the serialized DOM after
executing the editing operation, as it's done in the WPT editing tests,
which fail only in chrome, described in the bug report.

We only have hit by the bug when we implemented the "white-space"
property as a shorthand, as part of the CSS Text L4 spec, which is
correct, but we need to consider it when reconstructing the DOM tree
after certain editing operations.

The proposed solution is to define a new method in the
CSSPropertyValueSet to remove the equivalent properties; in the case of
the ones getting their value from a shorthand, they are only removed if
all its associated longhands are equivalent. This function will be only
used, for now, in the inline-style reconstruction logic performed as
part of the ReplaceSelectionCommand operations. We may want to apply it
to other editing-related operations in the future, and perhaps it'd make
sense to integrate it in the common RemoveEquivalentProperties method of
the CSSPropertyValueSet class.

Bug: 483903178
Change-Id: I0b72dc6a32c8e5be5fceb5df5a802e85e9fe4a46
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/7511015
Reviewed-by: Anders Hartvoll Ruud <andruud@chromium.org>
Reviewed-by: Stephen Chenney <schenney@chromium.org>
Reviewed-by: Dan Clark <daniec@microsoft.com>
Commit-Queue: Javier Fernandez <jfernandez@igalia.com>
Cr-Commit-Position: refs/heads/main@{#1592297}