Support TextMetrics API

[yisibl]

https://developer.mozilla.org/en-US/docs/Web/API/TextMetrics

• actualBoundingBoxAscent
• actualBoundingBoxDescent
• actualBoundingBoxLeft
• actualBoundingBoxRight
• alphabeticBaseline
• emHeightAscent
• emHeightDescent
• fontBoundingBoxAscent
• fontBoundingBoxDescent
• hangingBaseline
• ideographicBaseline
• width