Document fontSize default lineHeight object syntax

[olets]

The font-size documentation says that a default line-height can be given with [<font-size>, <line-height>], and that when specifying both a default line-height and a default letter-spacing the defaults go in an object:

[<font-size>, {
  letterSpacing: <letter-spacing>,
  lineHeight: <line-height>
}]

Support for using an object when specifying a default line-height without a default letter-spacing is undocumented.

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[adamwathan]

Thanks.