build_emoji: Generate emoji names and codepoints from emoji_map.

Replaces the hardcoded list of emoji_names and unicode_emoji_names in
static/js/emoji.js with a list generated from emoji_map.json, both to get
the list out of version control and so we can start modifying it for our
autocomplete. This does not change the contents of emoji_names. It sorts and
removes duplicates from unicode_emoji_names (causes no change in behavior,
since unicode_emoji_names is only used as if it were a set).

frontend_tests/node_tests/echo.js

@@ -30,6 +30,7 @@ set_global('page_params', {
 
 add_dependencies({
     marked: 'third/marked/lib/marked.js',
+    emoji_codes: 'generated/emoji/emoji_codes.js',
     emoji: 'js/emoji.js',
     people: 'js/people.js',
     stream_data: 'js/stream_data.js',

frontend_tests/node_tests/templates.js

@@ -6,6 +6,7 @@ set_global('page_params', {realm_emoji: {
 add_dependencies({
     Handlebars: 'handlebars',
     templates: 'js/templates',
+    emoji_codes: 'generated/emoji/emoji_codes.js',
     emoji: 'js/emoji',
     i18n: 'i18next',
 });