[animation-triggers-1] Add animation triggers 1 (#13571)

* Move text from css-animations-2 into animation-triggers-1

* Adde the changes

* Some cleanup and fixes

* Added intro and some fixes

* Remove unrelated copy-pasta and organize text

* Cleanup

* Edited the other-specs section

* Fix warnings and indent

Author: ydaniv

.gitignore

@@ -20,3 +20,4 @@ node_modules
 css-color-4/ICCprofiles/old-Display P3.icc
 
 .vscode
+.idea