[flang] Set polymorphic entity lowering option on by default

Preliminary patch for llvm#83285
to turn polymorphism on by default.

Will give a few days warning for people to remove the flag from their
workflow using flang-new.

Also easier to revert if issues with the gfortran test suites.

Author: jeanPerier

flang/include/flang/Lower/LoweringOptions.def

@@ -24,8 +24,8 @@ LOWERINGOPT(Name, Bits, Default)
 /// If true, lower transpose without a runtime call.
 ENUM_LOWERINGOPT(OptimizeTranspose, unsigned, 1, 1)
 
-/// If true, enable polymorphic type lowering feature. Off by default.
-ENUM_LOWERINGOPT(PolymorphicTypeImpl, unsigned, 1, 0)
+/// If true, enable polymorphic type lowering feature. On by default.
+ENUM_LOWERINGOPT(PolymorphicTypeImpl, unsigned, 1, 1)
 
 /// If true, lower to High level FIR before lowering to FIR. On by default.
 ENUM_LOWERINGOPT(LowerToHighLevelFIR, unsigned, 1, 1)

flang/test/Driver/flang-experimental-polymorphism-flag.f90

@@ -1,10 +1,10 @@
 ! Test -flang-experimental-hlfir flag
 ! RUN: %flang_fc1 -flang-experimental-polymorphism -emit-fir -o - %s | FileCheck %s
-! RUN: not %flang_fc1 -emit-fir -o - %s 2>&1 | FileCheck %s --check-prefix NO-POLYMORPHISM
+! RUN: %flang_fc1 -emit-fir -o - %s 2>&1 | FileCheck %s --check-prefix NO-POLYMORPHISM
 
 ! CHECK: func.func @_QPtest(%{{.*}}: !fir.class<none> {fir.bindc_name = "poly"})
 subroutine test(poly)
   class(*) :: poly
 end subroutine test
 
-! NO-POLYMORPHISM: not yet implemented: support for polymorphic types
+! NO-POLYMORPHISM: func.func @_QPtest