[css-values-3] Support for q unit

[Gérard Talbot]

Tests
-----

Only div#t3 and div#t4 in
http://w3c-test.org/css/css-values/absolute-length-units-001.html

http://w3c-test.org/css/css-values/q-unit-case-insensitivity-001.html

http://w3c-test.org/css/css-values/q-unit-case-insensitivity-002.html


Those 3 tests fail in Safari 12, in Safari Technology Preview and in WebKit Nightly Build (Epiphany Technological Preview 3.31.90-45-ga15d70306 with WebKitGTK 2.23.3):

https://wpt.fyi/results/css/css-values/absolute-length-units-001.html?label=stable

https://wpt.fyi/results/css/css-values/absolute-length-units-001.html?label=master

https://wpt.fyi/results/css/css-values/q-unit-case-insensitivity-001.html?label=stable

https://wpt.fyi/results/css/css-values/q-unit-case-insensitivity-001.html?label=master

https://wpt.fyi/results/css/css-values/q-unit-case-insensitivity-002.html?label=stable

https://wpt.fyi/results/css/css-values/q-unit-case-insensitivity-002.html?label=master

[Gérard Talbot]

I searched for a duplicate and did not find any.

[Radar WebKit Bug Importer]

<rdar://problem/48382426>

[Simon Fraser (smfr)]

*** This bug has been marked as a duplicate of bug 203469 ***