[Tracking] Modern focus / non-focus stroke rendering for Net11 editable controls (TextBoxBase)

[ricardobossan]

Related #14906
Give VisualStylesMode.Net11 editable controls (TextBox, MaskedTextBox, RichTextBox) a proper per-state border stroke: light side/top, a stronger bottom elevation edge, an accent bottom edge on focus, plus hover, disabled, and read-only treatments, all independent of ForeColor and composited in linear light.

Implemented by PR #14919. This sub-issue tracks that work and its fine-tuning for RC2.

Remaining fine-tuning:

• Focus bottom should grow strictly outward (not symmetrically) so it never overlaps the text area.