avmedia: Use appropriate OUString functions on string constants

Change-Id: I1abbe02b6a449d61d6bed5a7659f81ec4cf985fe
basic: Use appropriate OUString functions on string constants

Change-Id: Ied7e5eba39672363065083493bd5e60449fda371
comphelper: Use appropriate OUString functions on string constants

Change-Id: Ia09f122d4d968318fc0208b64b9bf7a0bc131f8a
cppuhelper: Use appropriate OUString functions on string constants

Change-Id: I7957898ed3172e79888bdb793e304359b10d75d7
cpputools: Use appropriate OUString functions on string constants

Change-Id: Iea0f7b4ee3ef867a061c159d90efb5d210ae92a4