[flang] Add missing source location to a semantic error message

[klausler]

Summary

Ensure that the semantic error "An allocatable or pointer component
reference must be applied to a scalar base" is emitted with a source
code location.

[PeteSteinfeld]

All builds and tests correctly and looks good.

flang/lib/Semantics/expression.cpp

       return std::nullopt;
     } else if (std::optional<DataRef> dataRef{
                    ExtractDataRef(std::move(*dtExpr))}) {
+      auto restorer{GetContextualMessages().SetLocation(name)};
       if (auto component{
               CreateComponent(std::move(*dataRef), *sym, *dtSpec->scope())}) {
         return Designate(DataRef{std::move(*component)});

flang/test/Semantics/expr-errors04.f90

     complex :: c, c2(2)
     integer :: x, x2(2)
     character(10) :: s, s2(2)
+    real, pointer :: p
+    real, allocatable :: a
    contains
     procedure, nopass :: info1 => real_info1
     procedure, nopass :: info2 => real_info2

   !ERROR: Reference to rank-2 object 't1' has 1 subscripts
   call t%t3%t2%t1(1:)%g1
 
+  !ERROR: An allocatable or pointer component reference must be applied to a scalar base
+  print *, t(1)%t3(1)%t2(1)%t1%p
+  !ERROR: An allocatable or pointer component reference must be applied to a scalar base
+  print *, t%t3(1)%t2(1)%t1(1,1)%p
+  !ERROR: An allocatable or pointer component reference must be applied to a scalar base
+  print *, t(1)%t3(1)%t2(1)%t1%a
+  !ERROR: An allocatable or pointer component reference must be applied to a scalar base
+  print *, t%t3(1)%t2(1)%t1(1,1)%a
+  !ERROR: An allocatable or pointer component reference must be applied to a scalar base
+  t(1)%t3(1)%t2(1)%t1%p => null()
+  !ERROR: An allocatable or pointer component reference must be applied to a scalar base
+  t%t3(1)%t2(1)%t1(1,1)%p => null()
+
 end