Update search for colon-syntax emoji to ignore case (#3443)

* Add tests for existing replaceColons functionality

* Update to lowercase before matching short names

* Update lib_test.ts

ts/components/emoji/lib.ts

@@ -255,6 +255,7 @@ export function replaceColons(str: string) {
   return str.replace(/:[a-z0-9-_+]+:(?::skin-tone-[1-5]:)?/gi, m => {
     const [shortName = '', skinTone = '0'] = m
       .replace('skin-tone-', '')
+      .toLowerCase()
       .split(':')
       .filter(Boolean);