Special:AllMessages: Ignore case of first letter when sorting

When a message key is defined with a upper case letter the sorting in
Special:AllMessages gets confused, because the upper case letter is
sorted before the lower case letters. Doing the upper case first, than
sorting avoids this when having such a key.

Bug: T86139
Change-Id: I8e9f7ca276a2fa999d8bd41c948cc083964ec66d