Add language version /to links that tools can link to (#6386)

firebase.json

@@ -374,6 +374,8 @@
       { "source": "/to/doc-comment-references", "destination": "/tools/doc-comments/references", "type": 301 },
       { "source": "/to/downgrade-testing", "destination": "/tools/pub/dependencies#test-with-downgraded-dependencies", "type": 301 },
       { "source": "/to/enforce-lockfile", "destination": "/tools/pub/packages#get-dependencies-for-production", "type": 301 },
+      { "source": "/to/language-version", "destination": "/resources/language/evolution#language-versioning", "type": 301 },
+      { "source": "/to/language-version-override", "destination": "/resources/language/evolution#per-library-language-version-selection", "type": 301 },
       { "source": "/to/main-function", "destination": "/language/functions#main", "type": 301 },
       { "source": "/to/package-discontinue", "destination": "/tools/pub/publishing#discontinue", "type": 301 },
       { "source": "/to/package-retraction", "destination": "/tools/pub/publishing#retract", "type": 301 },