Fix missing thin outlines in BDN XML / Blu-ray SUP export

[niksedk]

Fixes #12206

At small outline widths (1–2) the outline vanished on horizontal glyph edges (top of T, E, H, …) in image-based exports, varying with font and font size — e.g. Franklin Gothic/Arial at size 44 lost top outlines while other sizes lost horizontal or vertical ones. v4.0.16 rendered the same settings correctly.

Root cause

Two compounding problems in ImageRenderer.RenderTextToCanvas:

1. The outline stroke was centered on the glyph edge, so only outlineWidth / 2 extended outside the glyph — and the fill drawn on top covered the inner half. At width 1, only half a pixel of outline could ever be visible.
2. Stroking through the glyph rasterizer applies font hinting, which snaps horizontal edges to the pixel grid. The surviving half-pixel rim landed in the same pixel row as the fill's antialiased edge, and the opaque fill blended over it — leaving ~50% alpha light-gray pixels (rgba(169,169,169,130)) instead of a black outline. Whether anything survives depends on where the cap-height edge lands on the pixel grid, which explains the font/size dependence reported in the issue.

Fix

• Build the shaped text outline as an SKPath (via SKShaper glyph positions, preserving HarfBuzz shaping) and stroke the path directly, bypassing the hinted glyph rasterizer.
• Stroke with 2× the requested width — the fill covers the inner half, so the visible outline matches the requested width (same semantics as ASSA/libass and v4's GDI+ path rendering).
• Disable hinting on export fonts so the fill edges stay registered with the raw path geometry (export renders at video resolution; hinting is not needed).

The same treatment is applied to the shadow outline pass. Glyphs without outline paths (e.g. color emoji) simply get no stroke; fills are unchanged.

Verification

Headless harness calling ImageRenderer.GenerateBitmap with white text / black outline width 1, "THE HEIGHT", Arial/Tahoma/Helvetica at sizes 44/45/53. Per-column check for outline pixels above the topmost fill pixel:

	Columns missing top outline
Before	~98–100% in every font/size combination
After	0 in every combination

Visual inspection at 4× zoom confirms a clean, uniform 1px outline on all edges, and a styled sample (bold/italic/font color + shadow + outline) renders correctly. LibUiLogicTests (6) and SeConvTests (217) pass.

🤖 Generated with Claude Code