Add ring and promote methods for Constant objects

Add support for creating matrices with Constant entries.  Also add a
unit test.

M2/Macaulay2/m2/reals.m2

@@ -270,6 +270,11 @@ EulerConstant = new Constant from { symbol EulerConstant, mpfrConstantEuler, eRR
 CatalanConstant = new Constant from { symbol CatalanConstant, mpfrConstantCatalan, cRRi0}
 ii = new Constant from { symbol ii, ConstantII}
 
+ring Constant := ring @@ numeric
+promote(Constant, InexactNumber') :=
+promote(Constant, RingElement)    := (x, R) -> (
+    promote(numeric(precision R, x), R))
+
 isFinite Constant := x -> true
 
 lngamma = method()

M2/Macaulay2/tests/normal/matrix.m2

@@ -371,6 +371,9 @@ scan({matrix {}, matrix(ZZ, {}), map(ZZ^0, ZZ^0, {}), map(ZZ^0,, {})}, A -> (
 	    assert Equation(source A, ZZ^0);
 	    assert Equation(target A, ZZ^0)))
 
+-- issue #3456
+assert Equation(matrix {{ii}}, matrix {{numeric ii}})
+
 -- Local Variables:
 -- compile-command: "make -C $M2BUILDDIR/Macaulay2/packages/Macaulay2Doc/test matrix.out"
 -- End:

M2/Macaulay2/tests/normal/numbers.m2

@@ -126,6 +126,8 @@ assert( promote(1,RR) === 1. )
 assert( promote(1,RR_222) === 1p222 )
 assert( promote(1/1,RR) === 1. )
 assert( promote(1/1,RR_222) === 1p222 )
+assert( promote(pi, RR_222) === numeric(222, pi) )
+assert( promote(pi, RR_222[x]) == numeric(222, pi) )
 
 assert( promote(1,CC) == 1 )
 assert( promote(1,CC) == 1. )
@@ -143,6 +145,10 @@ assert( promote(1.,CC) == 1. )
 assert( promote(1.,CC) === 1.+0*ii )
 assert( promote(1.,CC_222) === toCC 1p222 )
 assert( promote(1.,CC_222) === toCC 1p222 )
+assert( promote(pi, CC_222) === toCC(222, numeric(222, pi), 0.0) )
+assert( promote(ii, CC_222) === toCC(222, 0, 1) )
+assert( promote(pi, CC_222[x]) == numeric(222, pi) )
+assert( promote(ii, CC_222[x]) == toCC(222, 0, 1 ) )
 assert( not liftable(+ii,RR) )
 assert( liftable(0*ii,RR) )
 assert( lift(3.5,QQ) === 7/2 )