KFileWidget: Allow saving single file with double quotes

Akseli Lahtinenrequested to merge
work/akselmo/allow-saving-with-double-quotes into master

The tokenizer would previously remove any and all double quotes, so saving with them would be impossible.

In cases where we're saving only one file, make sure to escape the double quotes for the tokenizer to know they should be kept around

BUG: 426728

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