Functions: Expose set_all method for generic virtual arrays

This is very similar to rB5613c61275fe6 and rB0061150e4c90d, basically
just exposing a `VMutableArray` method to its generic counterpart. This
is quite important for curve point attributes to avoid a lookup for
every point when there are multiple splines.

source/blender/functions/FN_generic_virtual_array.hh

@@ -220,11 +220,19 @@ class GVMutableArray : public GVArray {
 
   void fill(const void *value);
 
+  /* Copy the values from the source buffer to all elements in the virtual array. */
+  void set_all(const void *src)
+  {
+    this->set_all_impl(src);
+  }
+
  protected:
   virtual void set_by_copy_impl(const int64_t index, const void *value);
   virtual void set_by_relocate_impl(const int64_t index, void *value);
   virtual void set_by_move_impl(const int64_t index, void *value) = 0;
 
+  virtual void set_all_impl(const void *src);
+
   virtual void *try_get_internal_mutable_varray_impl();
 };
 
@@ -554,6 +562,11 @@ template<typename T> class GVMutableArray_For_VMutableArray : public GVMutableAr
     varray_->set(index, std::move(value_));
   }
 
+  void set_all_impl(const void *src)
+  {
+    varray_->set_all(Span((T *)data, size_));
+  }
+
   void materialize_impl(const IndexMask mask, void *dst) const override
   {
     varray_->materialize(mask, MutableSpan((T *)dst, mask.min_array_size()));

source/blender/functions/intern/generic_virtual_array.cc

@@ -160,6 +160,19 @@ void GVMutableArray::set_by_relocate_impl(const int64_t index, void *value)
   type_->destruct(value);
 }
 
+void GVMutableArray::set_all_impl(const void *src)
+{
+  if (this->is_span()) {
+    const GMutableSpan span = this->get_internal_span();
+    type_->copy_to_initialized_n(src, span.data(), size_);
+  }
+  else {
+    for (int64_t i : IndexRange(size_)) {
+      this->set_by_copy(i, POINTER_OFFSET(src, type_->size() * i));
+    }
+  }
+}
+
 void *GVMutableArray::try_get_internal_mutable_varray_impl()
 {
   return nullptr;