FLEDGE: Enable screen height as unit and pure numbers input for ad

size.

Currently, for generateBid() and joinAdInterestGroup(), the supported
ad size units are
* "px": pixel
* "sw": screen width

This CL adds the unit:
* "sh": screen height

The parser is also updated to support parsing pure numbers as pixels.
For example, "100" is parsed as 100 pixels.

A regular expression is used to match the input, and capture the
sub-patterns for value and unit.
^\s*((?:0|(?:[1-9][0-9]*))(?:\.[0-9]+)?)(px|sw|sh)?\s*$

It basically means we match
1. Zero or more leading spaces.
2. Numbers, with optionally decimal point and digits. No leading space, cannot begin with zero, non-negative. (Sub-pattern captured)
3. Immediately followed by an unit which can be one of "px", "sw" or "sh", or the unit can be ignored entirely.
entirely. (Sub-pattern captured)
4. Zero or more trailing spaces.

Bug: http://b/239866637

See Turtledove issue: WICG/turtledove#312
See Turtledove PR: WICG/turtledove#417

Change-Id: I336055ff3dd635dcdfd78999d0cb5972569f5ac1

fenced-frame/fledge-container-size.https.html

@@ -89,9 +89,6 @@
 }
 
 // Type error cases.
-promise_test(async () => { return checkSyntaxError('299', '72'); }, '299 x 72');
-promise_test(async () => { return checkSyntaxError('299px', '72'); }, '299px x 72');
-promise_test(async () => { return checkSyntaxError('299', '72px'); }, '299 x 72px');
 promise_test(async () => { return checkSyntaxError('-299px', '72px'); }, '-299px x 72px');
 promise_test(async () => { return checkSyntaxError('299px', '-72px'); }, '299px x -72px');
 promise_test(async () => { return checkSyntaxError('0px', '0px'); }, '0px x 0px');