Bug 6180 - Parser: Backslash double-quote in double-quoted string not recognized

This is a simplistic cherry-pick from Boron:

Statement parser removes all double or single quotes from strings,
what is incorrect. This fix removes only first and last quotes if they are
present. All other quotes in the string should be escaped already, since the
ANTLR parser recognizes only correctly enclosed strings.

Further, substitution of backslash-escaped characters in
double-quoted strings is done.

Change-Id: I2f596c73be05178dc5cbebaed12e25e428454219
Signed-off-by: Peter Kajsa <pkajsa@cisco.com>
Signed-off-by: Vratko Polak <vrpolak@cisco.com>