getKerning method
Pair-kerning adjustment between two consecutive glyphs, in pixels.
Returns 0 if no kern pair is defined for the combination.
Implementation
double getKerning(int glyphId1, int glyphId2, double fontSize) {
final value = _kern[(glyphId1, glyphId2)] ?? 0;
return value * fontSize / metrics.unitsPerEm;
}