Move core of constant propagation domain to util/

This part of the constant propagator has no dependency on code outside
util and enables stateful expression simplification. Moving to util will
enable future use within language front-ends. This is only a
refactoring, with the exception of the output function, which now uses
format() instead of from_expr(), which required a change to the expected
test output in one case.

Author: tautschnig

jbmc/regression/janalyzer/string-initializer/test.desc

@@ -4,6 +4,6 @@ Basic1.class
 ^EXIT=0$
 ^SIGNAL=0$
 Hello_20 = \{ \.@class_identifier="java::java\.lang\.String" \};
-java::java\.lang\.String\.Literal\.Hello_20=\{ \.@class_identifier="java::java\.lang\.String" \}
+java::java\.lang\.String\.Literal\.Hello_20=\{ "java::java\.lang\.String" \}
 --
 ^warning: ignoring