Enable new Scintlla lexer.cpp.verbatim.strings.allow.escapes lexer property for ObjectiveC.
This allows custom filetypes to define a mime type, hence the icon displayed for this filetype; as well as moving ones for built-in filetypes out of the code to the configuration files.
Based on a patch from Elias Pschernig, thanks. Parser was taken from upstream CTags. Closes patch#3325139.