LibDebug: Add AttributeForm field to Dwarf::AttributeValue

In some contexts, it's helpful to also know the "Attribute Form",
in addition to the "Attribute Type".

An example for such context is the interpretation of the
"DW_AT_high_pc" attribute, which has different meaning if the form
is an address or a constant.

Userland/Libraries/LibDebug/Dwarf/DwarfInfo.cpp

@@ -5,6 +5,7 @@
  */
 
 #include "DwarfInfo.h"
+#include "AttributeValue.h"
 
 #include <AK/MemoryStream.h>
 
@@ -61,6 +62,7 @@ AttributeValue DwarfInfo::get_attribute_value(AttributeDataForm form, ssize_t im
     InputMemoryStream& debug_info_stream, const CompilationUnit* unit) const
 {
     AttributeValue value;
+    value.form = form;
 
     auto assign_raw_bytes_value = [&](size_t length) {
         value.data.as_raw_bytes.length = length;