Get detailed font metrics

[Zedas74]

Feature Request

Feature description

I would like to have more font metric information to render initials, etc. in form of a few getter functions.

The new methods should be placed after the currentLineHeight(includeGap) method in the pdfkit/lib/mixins/fonts.js file.

I already use them locally:

currentFontAscender() { return (this._font.ascender) / 1000 * this._fontSize; },
currentFontDescender() { return (this._font.descender) / 1000 * this._fontSize; },
currentFontLineGap() { return (this._font.lineGap) / 1000 * this._fontSize; },
currentFontXHeight() { return (this._font.xHeight) / 1000 * this._fontSize; },
currentFontCapHeight() { return (this._font.capHeight) / 1000 * this._fontSize; },