[flang] Allow nested scopes for implied DO loops with DATA statements (llvm#129410)

Previously, nested scopes for implied DO loops with DATA statements were
disallowed, which meant that the following code couldn't compile due to
re-use of `j` loop variable name:
    
    DATA (a(i),(b(i,j),j=1,3),(c(i,j),j=1,3),i=0,4)/
    
This change allows nested scopes implied DO loops, which allows the code
above to compile.

Tests modified to in accordance with this change:
Semantics/resolve40.f90, Semantics/symbol09.f90

Author: eugeneepshteyn

flang/lib/Semantics/resolve-names.cpp

@@ -7490,15 +7490,10 @@ bool ConstructVisitor::Pre(const parser::DataImpliedDo &x) {
   Walk(bounds.upper);
   Walk(bounds.step);
   EndCheckOnIndexUseInOwnBounds(restore);
-  bool pushScope{currScope().kind() != Scope::Kind::ImpliedDos};
-  if (pushScope) {
-    PushScope(Scope::Kind::ImpliedDos, nullptr);
-  }
+  PushScope(Scope::Kind::ImpliedDos, nullptr);
   DeclareStatementEntity(bounds.name, type);
   Walk(objects);
-  if (pushScope) {
-    PopScope();
-  }
+  PopScope();
   return false;
 }
 
@@ -7539,9 +7534,9 @@ bool ConstructVisitor::Pre(const parser::DataStmtObject &x) {
             }
           },
           [&](const parser::DataImpliedDo &y) {
-            PushScope(Scope::Kind::ImpliedDos, nullptr);
+            // Don't push scope here, since it's done when visiting
+            // DataImpliedDo.
             Walk(y);
-            PopScope();
           },
       },
       x.u);

flang/test/Semantics/resolve40.f90

@@ -69,8 +69,8 @@ subroutine s8
 
 subroutine s9
   real :: x(2,2)
-  !ERROR: 'i' is already declared in this scoping unit
-  data ((x(i,i),i=1,2),i=1,2)/4*0.0/
+  ! Nested implied DO loops have their own scope
+  data ((x(i,j),j=1,2),(x(i,j),j=1,2),i=1,2)/8*0.0/
 end
 
 module m10

flang/test/Semantics/symbol09.f90

@@ -51,7 +51,7 @@ subroutine s3
  real, dimension(n,n) :: x
  !REF: /s3/x
  !DEF: /s3/ImpliedDos1/k (Implicit) ObjectEntity INTEGER(4)
- !DEF: /s3/ImpliedDos1/j ObjectEntity INTEGER(8)
+ !DEF: /s3/ImpliedDos1/ImpliedDos1/j ObjectEntity INTEGER(8)
  !REF: /s3/n
  !REF: /s3/n2
  data ((x(k,j),integer(kind=8)::j=1,n),k=1,n)/n2*3.0/