text: project kerning offset onto rotated text-flow axis

[benface]

Fixes #1045.

Summary

draw_text_ex always adds kerning_offset to dest.x, ignoring TextParams.rotation. At rotation = 0 text flows along +X and that's correct; at rotation = π / 2 text flows along +Y so the offset lands perpendicular to the text-flow axis. Multiplying by (rot_cos, rot_sin) routes the offset into the correct axis for any rotation.

Cause

In draw_text_ex:

let rot_cos = rot.cos();
let rot_sin = rot.sin();
let dest_x = (offset_x + total_width) * rot_cos + (glyph_scaled_h + offset_y) * rot_sin;
let dest_y = (offset_x + total_width) * rot_sin + (-glyph_scaled_h - offset_y) * rot_cos;

let dest = Rect::new(
    dest_x / dpi_scaling + x + kerning_offset / dpi_scaling,  // ← always +X
    dest_y / dpi_scaling + y,                                  //   never +Y
    ...
);

(offset_x + total_width) accumulates along the unrotated text-flow axis (+X in glyph-local space) and the rotation matrix correctly routes it into dest_x / dest_y. The kerning offset is an additional text-flow advance but gets added to dest.x without the same routing.

Fix

Project kerning_offset (logical-pixel-converted, same as the existing / dpi_scaling) onto the rotation basis vectors:

let kerning_logical = kerning_offset / dpi_scaling;
let dest = Rect::new(
    dest_x / dpi_scaling + x + kerning_logical * rot_cos,
    dest_y / dpi_scaling + y + kerning_logical * rot_sin,
    ...
);

At rotation = 0: rot_cos = 1, rot_sin = 0 → identical to the previous behaviour.
At rotation = π / 2: rot_cos = 0, rot_sin = 1 → offset routes into dest.y.
Any other angle: offset projects onto the rotated flow direction.

total_width += char_data.advance * font_scale_x + kerning_offset; (line 386) is unchanged — total_width stays in unrotated glyph-local space and is itself routed through the rotation matrix on the next iteration.

Verification

Tested with the originally-reported reproducer: a font with kerning entries (OstrichSans-Heavy) drawn at rotation = π / 2. Before the patch, kerned pairs in strings like RESTART LEVEL show per-character perpendicular shifts in screen space that vary with the surrounding kerning context. With the patch, the shift disappears and the rotated text reads as a clean baseline.

[benface]

FYI: the failing wasm32-unknown-unknown job is a pre-existing master regression — also red on ed9cdbd, dce417ad, and dd57be6 (this PR's base). Last green CI on master was 44afa9d. Other five jobs pass.

[not-fl3]

Thanks for PR!