2-SCM fixes

[niegowski]

Suggested merge commit message (convention)

Fix (html-support): The DocumentSelection should not store the GHS linkA attribute if the linkHref attribute was removed by the two-step caret movement feature. Closes #15051.

Other (link, typing): The logic behind the two-step caret movement extracted to the common code in the two-step caret movement feature.

Other (typing): Unified behavior of the insertText command for cases using the DocumentSelection and Selection as applied attributes behaved differently in those cases.

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Additional information

The behavior of typing over the fully-selected formatted text content (for example foo <b>[bar]</b> baz) was changing over time.

Initially the insertText (previously known as input) command inserted text without a bold attribute (if the formatted part was fully selected before typing).

After migration to the beforeInput events, this behavior changed as a side effect of using the targetRanges instead of the DocumentSelection. The Selection provided for the command was not related to the DocumentSelection and selection attributes behaved differently depending on whether the DocumentSelection or Selection was provided to the command.

In this PR I fixed the case of mixed behavior. I decided to keep the current behavior for two reasons.

• First, it is how it works now (the insertText command receives the selection to override the content).
• Second, in the LinkEditing we had a custom logic to be able to type over a link and replace the text label of the link without removing the link itself. It looks reasonable to me.