MDL-76440 editor_tiny: Reset text-align to initial

Bootstrap core's "reboot" sets a default text-align which is
incompatible with RTL languages.

Arguably this should be set in the Boost theme, but this is a fairly
large change which has potential to break things so I'm making it here
where we experience the issue for now.

lib/editor/tiny/editor_styles.css

@@ -1,3 +1,4 @@
 body.mce-content-body {
     margin: revert;
+    text-align: initial;
 }