[FIX] sap.m.CheckBox: Test page adjusted
[FIX] sap.m.CheckBox: Test page adjusted

Test page was corrected in such a way, that it could fully
follow the accessibility guidelines.

This includes:

- Removed explict width on RTL checkbox, since it was too
  small for the whole text
- Fixed a typo in the same checkbox
- Provided a title for the form

BCP: 1880228149, 1880228060

Change-Id: Ie4b48be45e90e77cc0bc83bd774683a26d5d0bbd

cschuff/openui5,SAP/openui5,cschuff/openui5,cschuff/openui5,SAP/openui5,SAP/openui5,SAP/openui5