PSA: Add missing unit value functions to numeric factory for the CSS typed OM api

[Rune Lillesveen]

Only a selection of font relative and resolution units have been made available on the CSS api in javascript for numeric factory methods when shipped as new units.

These methods are shorter alternatives to the constructors. E.g.

CSS.ex(10);

instead of:

new CSSUnitValue(10, "ex");

The new units were shipped as per intents below, but as an oversight not exposed through the numeric factory CSS idl. I don't expect that these additions will break anything. Firefox do not support any of these, but Safari support the units they ship, but they do not support all root units in general.

I plan to expose the following units to the CSS api:

ic: https://groups.google.com/a/chromium.org/d/msgid/blink-dev/CACuPfeRZ3eVkzxZxv%2B_Km9JbBpDRL0Omcxcf9fyc6NmZf19nqQ%40mail.gmail.com
lh: https://groups.google.com/a/chromium.org/d/msgid/blink-dev/CACuPfeRke__t9Piz-JRuy0qW_RNNao8CNS32F0XM_%3DcRYj6FYw%40mail.gmail.com
rex/rch/ric/rlh : https://groups.google.com/a/chromium.org/d/msgid/blink-dev/CAK_fkKV3D8Gpno7mie4LD5B%2BNiGvjfnRvAtJ5rsiBWYL8Mv2Bw%40mail.gmail.com
cap/rcap: https://groups.google.com/a/chromium.org/g/blink-dev/c/jiuxWVJEmqs/m/u0dMUmA4AwAJ
x: https://groups.google.com/a/chromium.org/g/blink-dev/c/FsD97U77tss

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Rune Lillesveen