Accept minor and patch versions in targets

[marcoroth]

This pull request updates targets to accept a minor or patch version for each browser, so a call can target a release like Safari 15.4.

An Integer still means a major version. A Float or a String now also sets the minor and patch versions, encoded as major << 16 | minor << 8 | patch, the same encoding the Node binding uses.

LightningCSS.transform(".a { color: oklch(60% .2 30) }", targets: { safari: 15 }, minify: true).code
#=> ".a{color:lab(51.6908% 61.9679 48.0969)}"

LightningCSS.transform(".a { color: oklch(60% .2 30) }", targets: { safari: 15.4 }, minify: true).code
#=> ".a{color:oklch(60% .2 30)}"

LightningCSS.transform(".a { color: oklch(60% .2 30) }", targets: { ios_saf: "15.4.1" }, minify: true).code
#=> ".a{color:oklch(60% .2 30)}"

A Float loses a minor version above 9, since 16.10 is 16.1, so we recommend using a String instead.

A version that doesn't parse raises a LightningCSS::OptionError that names the browser:

LightningCSS.transform(".a{}", targets: { safari: "15.a" })
#=> LightningCSS::OptionError: Invalid version "15.a" for safari in targets

Resolves #16