feat: allow passing in only icon SVG data to addIcons

[liamdebeasi]

See https://github.com/ionic-team/ionic-framework-design-documents/commit/a12daf314e9fdd6619503e88e9c99d2c184d95b7

This feature allows developers to pass icons to the icon map without explicitly setting the string name. This cuts down on boilerplate and reduces the likelihood of mapping the icon to a typo (i.e. "log-ionic" instead of "logo-ionic")

For backwards compatibility purposes, the camel case key will still be available for developers who are explicitly mapping icon SVG data to camel case keys.

As part of this, Ionicons will now warn if multiple icons are mapped to the same key. TypeScript should prevent devs from explicitly doing this in Objects, but by autogenerating keys this may happen without the developer knowing. A warning will be logged so devs are aware of when this happens.

Usage

/**
 * Yields "logo-ionic" and "logoIonic" keys in the map
 */
addIcons({ 'logoIonic': logoIonic });

/**
 * Yields "logo-ionic" key in the map
 */
addIcons({ 'logo-ionic': logoIonic });

/**
 * Yields "logo-ionic" and "logoIonic" keys in the map
 */
addIcons({ logoIonic });

/**
 * "logo-a" key maps to logoB object, and a warning is logged for the logoA object.
 */
addIcons({ 'logo-a': logoB, logoA });

[sean-perkins]

Updated the base branch to target a feature-7.2 branch so we can group updates for the next release.