is_{Real,Complex}[Double]Field: In doctests, add deprecation warning to expected output

Author: Matthias Koeppe

src/sage/rings/complex_double.pyx

@@ -123,6 +123,10 @@ def is_ComplexDoubleField(x):
 
         sage: from sage.rings.complex_double import is_ComplexDoubleField
         sage: is_ComplexDoubleField(CDF)
+        doctest:warning...
+        DeprecationWarning: is_ComplexDoubleField is deprecated;
+        use isinstance(..., sage.rings.abc.ComplexDoubleField) instead
+        See https://trac.sagemath.org/32610 for details.
         True
         sage: is_ComplexDoubleField(ComplexField(53))
         False

src/sage/rings/complex_mpfr.pyx

@@ -169,6 +169,10 @@ def is_ComplexField(x):
 
         sage: from sage.rings.complex_mpfr import is_ComplexField as is_CF
         sage: is_CF(ComplexField())
+        doctest:warning...
+        DeprecationWarning: is_ComplexField is deprecated;
+        use isinstance(..., sage.rings.abc.ComplexField) instead
+        See https://trac.sagemath.org/32610 for details.
         True
         sage: is_CF(ComplexField(12))
         True

src/sage/rings/real_double.pyx

@@ -84,6 +84,10 @@ def is_RealDoubleField(x):
 
         sage: from sage.rings.real_double import is_RealDoubleField
         sage: is_RealDoubleField(RDF)
+        doctest:warning...
+        DeprecationWarning: is_RealDoubleField is deprecated;
+        use isinstance(..., sage.rings.abc.RealDoubleField) instead
+        See https://trac.sagemath.org/32610 for details.
         True
         sage: is_RealDoubleField(RealField(53))
         False

src/sage/rings/real_mpfr.pyx

@@ -5906,6 +5906,10 @@ def is_RealField(x):
     EXAMPLES::
 
         sage: sage.rings.real_mpfr.is_RealField(RR)
+        doctest:warning...
+        DeprecationWarning: is_RealField is deprecated;
+        use isinstance(..., sage.rings.abc.RealField) instead
+        See https://trac.sagemath.org/32610 for details.
         True
         sage: sage.rings.real_mpfr.is_RealField(CC)
         False