Compile-time lookup of the Carbon icons.
The 32px SVGs from the @carbon/icons npm package (install it in your
app: npm install --prefix assets @carbon/icons) are read at compile time and stored as a map of
icon name to inner SVG markup. They scale to any size, so only the 32px
variant is embedded.
If the npm package is not installed when compiling, the lookup is empty and
CarbonPhoenix.CoreComponents.icon/1 renders an empty <svg>.