[css-typed-om]: CSSCalcDictionary needs a different name

[annevk]

Per @bzbarsky, it's length-specific, whereas calc() can return a number.

[tabatkins]

Yeah, we need a family of calcs for each type. (It can also return an angle, a frequency...)

[shans]

Going to rename this CSSLengthCalcDictionary.

[shans]

Addressed by 647b44d