Encoding patch; please commit (#46178)

Hello!

HEAD Kate have a bug which annoys me since 3.0 was released.
Sometimes default encoding in KateFileDialog combo turns into 
pt154 (from my locale-default Cp 1251).
It's because KateFileDialog constructor assumes encoding 
parameter to be in QT form ("CP 1251") while it could be KGlobal 
style "Cp 1251". It is also interesting that KateFileDialog's 
own exec() returns "Cp 1251".
Patch for kfiledialog.cpp is attached (correctly accepts both 
capitalizations).

Also I've made some clean-up in KateViewManager removing 
m_encoding variable as unnecessary and compacting openURL 
method. Patches are also applied.

-- 

	best regards, V.S.G.