_buildKerningPairs( json ) {

		const friendlyKernings = {};

		// Loop through each kernings pairs defined in msdf json
		for ( let i = 0; i < json.kernings.length; i++ ) {

			const kerning = json.kernings[ i ];

			// ignore zero kerned glyph pair
			if ( kerning.amount === 0 ) continue;

			// Build and store the glyph paired characters "ij","WA", ... as keys, referecing their kerning amount
			const glyphPair = String.fromCharCode( kerning.first, kerning.second );

			// This would then be available for fast access
			friendlyKernings[ glyphPair ] = kerning.amount;

		}

		// update the font to keep it
		return friendlyKernings;

	}
Ensure that each font variant has its kerning dictionary
@see src/font/msdf/FontVariantMSDF.js for an implementation

@param {MSDFJson} json
@returns {import('../FontVariant').KerningPairs}
@private