fix emoji glyph placement on the terminal grid#1564
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Emoji rendered slightly upper-right of its 2-cell slot because
`grid_emit::ensure_glyph_by_id` rasterized at the text point size and
placed the bitmap on the primary font's baseline (`cell_h - ascent +
top`), using bearings from the emoji font's own coordinate system. The
two metric systems don't compose, so the offset was unavoidable for
any non-trivial emoji font.
Also fixes a related bug in `find_best_font_match{,_strict}`: the
symbol-map fast path hardcoded `is_emoji = false`, so config-pinned
emoji families (e.g. `Segoe UI Emoji` via `[fonts.symbol-map]`)
bypassed the emoji rasterization path entirely. Now inherits
`is_emoji` from the mapped font's color-table detection.
For emoji `ensure_glyph_by_id` now:
- rasterizes at `min(2*cell_w, cell_h)` so the bitmap fills its 2-cell
slot regardless of the text font size,
- buckets the atlas key by that cell-derived size so it doesn't alias
text rasterizations during resize,
- centers the bitmap horizontally in `2*cell_w` and vertically in
`cell_h` (matches the symbol-centering rationale in changelog 42 for
PUA constraint glyphs).
Hot path is unchanged — atlas lookups still hit on the first call per
emoji glyph and stay cached.
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Fixed #1563
grid_emit::ensure_glyph_by_idnow rasterizes color-emoji glyphs at a cell-derived size (min(2*cell_w, cell_h)) and centers the bitmap inside the 2-cell slot, instead of using the text point size and the primary font's baseline math (which mixes coordinate systems with the emoji font's own bbox).find_best_font_match{,_strict}now inheritsis_emojifrom the mapped font's color-table flag instead of hardcodingfalse, so config-pinned emoji families (e.g.Segoe UI Emojivia[[fonts.symbol-map]]) reach the emoji rendering path.The atlas is bucketed by the cell-derived size, so emoji glyphs cache the same way they always did and the per-frame hot path is unchanged.
Only the first rasterization of each emoji is marginally larger.