[qcms] Provide an API to compute xyY gamut area relative to NTSC 1953

The new API computes profile relative gamut area using (x,y) coordinates.
This feature will allow a better understanding of the nature of display
color profiles in use.

This patch contains a test case that displays the new metric for an
input profile and QCMS's internal sRGB profile.

qcms_tests -t qcms_test_ntsc_gamut -i AdobeRGB.icc
NTSC 1953 relative gamut area test
Input profile
	Description: Adobe RGB (1998)
	NTSC relative gamut area: 92.714 %
Internal reference profile
	Description: sRGB IEC61966-2.1
	NTSC relative gamut area: 68.946 %

BUG=582870

Review URL: https://codereview.chromium.org/1703553002

Cr-Commit-Position: refs/heads/master@{#375864}