various fixes to dojox/mobile/bidi code:

1. fix accidental creation of "config" global variable
2. fix summary of config module to appear in API doc
3. don't use deprecated dijit/_BidiSupport module; use new dijit/_BidiMixin

refs #15778

(cherry picked from commit 55265d8c567b54ad57bcc029f5e3d225171871f7)