DEV: Upgrade babel & remove vendored safari-bugfix transformation (#28208)

The Safari 15 bugfix has been rolled into @babel/preset-env in the most recent version, so we no longer need to carry our vendored copy.

This commit updates @babel/preset-env, runs npx yarn-deduplicate yarn.lock, and removes the vendored transform.

This commit also refactors our theme transpiler to use @babel/preset-env, with the same list of target browsers as our ember-cli build uses. This means we no longer need to maintain a separate list of babel transforms for themes.

lib/discourse_js_processor.rb

@@ -6,15 +6,6 @@ class DiscourseJsProcessor
   class TranspileError < StandardError
   end
 
-  # To generate a list of babel plugins used by ember-cli, set
-  # babel: { debug: true } in ember-cli-build.js, then run `yarn ember build -prod`
-  DISCOURSE_COMMON_BABEL_PLUGINS = [
-    ["decorator-transforms", { runEarly: true }],
-    "proposal-class-static-block",
-    "transform-parameters",
-    "proposal-export-namespace-from",
-  ]
-
   def self.ember_cli?(filename)
     filename.include?("/app/assets/javascripts/discourse/dist/")
   end
@@ -161,7 +152,6 @@ class DiscourseJsProcessor
           filename: logical_path || "unknown",
           extension: extension,
           themeId: theme_id,
-          commonPlugins: DISCOURSE_COMMON_BABEL_PLUGINS,
         },
       )
     end