support high contrast mode detection #424
Description
Most widgets don't need special code to support high-contrast mode, because when the user sets the OS to high-contrast mode, the browser automatically changes text color and font-size according to the OS's setting.
However, deliteful/ProgressIndicator is an exception because it uses SVG, and the browser does not adjust the colors within SVG DOM.
Therefore, add high-contrast detection code to delite, similar to dojo core's hccss.js.
Some possible debate points about this PR:
- should it set the CSS class on
<body>, or just define has("highcontrast")? - relatedly, should the code be in a separate hc.js module, or rolled into features.js?
See also ibm-js/deliteful#585.