[Android][B1] Compose Math() + bitmap cache (the flagship)

[clintecker]

@Composable Math(latex, display, color, modifier) drawing the vector display list on a Canvas, with a bitmap cache keyed by (latex, size, scale, color) — the key that structurally prevents the #17 raster scale-lock.

Acceptance

• Renders on a Canvas; re-themes/re-scales without re-typesetting.
• Cache hit on repaint; eviction bounded by count + pixel-space cost (port the NSCache cost accounting for rendered math images is in point-space, ignoring backing scale — undercounts real iOS bitmap memory up to 9x #5 fix — do NOT count in point space).
• TalkBack contentDescription from the spoken description carried across the boundary (design accessibility in from surface Linux backend passes the whole OTF (not the extracted MATH table) to MathTableParser, so all bundled fonts silently fall back to Latin Modern's constants #1).

Depends on: B0, A1.