Fix building with wxUSE_STL enabled in VS2019 16.6

Exporting standard C++ library types is not allowed any more, see

https://developercommunity.visualstudio.com/content/problem/1042081/142628801includexhash201332-error-c2338-this-funct.html

so don't use DLL export declarations for wxHash{Map,Set} classes, which
derive from std::{map,set}.

Since the classes are header-only, this should have no direct
consequences. Only classes that extend wxHashMap or wxHashSet, like
wxImageHistogram, have to be made header only as well.

Remove the wxLogError message in wxImageHistogram::FindFirstUnusedColour, so
log.h and translation.h do not have to be included in the header.

Closes https://github.com/wxWidgets/wxWidgets/pull/2009

include/wx/hashmap.h

@@ -678,24 +678,27 @@ public: \
 
 // and these do exactly the same thing but should be used inside the
 // library
+// note: DECL is not used since the class is inline
 #define WX_DECLARE_HASH_MAP_WITH_DECL( KEY_T, VALUE_T, HASH_T, KEY_EQ_T, CLASSNAME, DECL) \
-    _WX_DECLARE_HASH_MAP( KEY_T, VALUE_T, HASH_T, KEY_EQ_T, CLASSNAME, DECL )
+    _WX_DECLARE_HASH_MAP( KEY_T, VALUE_T, HASH_T, KEY_EQ_T, CLASSNAME, class )
 
 #define WX_DECLARE_EXPORTED_HASH_MAP( KEY_T, VALUE_T, HASH_T, KEY_EQ_T, CLASSNAME) \
     WX_DECLARE_HASH_MAP_WITH_DECL( KEY_T, VALUE_T, HASH_T, KEY_EQ_T, \
                                    CLASSNAME, class WXDLLIMPEXP_CORE )
 
+// note: DECL is not used since the class is inline
 #define WX_DECLARE_STRING_HASH_MAP_WITH_DECL( VALUE_T, CLASSNAME, DECL ) \
     _WX_DECLARE_HASH_MAP( wxString, VALUE_T, wxStringHash, wxStringEqual, \
-                          CLASSNAME, DECL )
+                          CLASSNAME, class )
 
 #define WX_DECLARE_EXPORTED_STRING_HASH_MAP( VALUE_T, CLASSNAME ) \
     WX_DECLARE_STRING_HASH_MAP_WITH_DECL( VALUE_T, CLASSNAME, \
                                           class WXDLLIMPEXP_CORE )
 
+// note: DECL is not used since the class is inline
 #define WX_DECLARE_VOIDPTR_HASH_MAP_WITH_DECL( VALUE_T, CLASSNAME, DECL ) \
     _WX_DECLARE_HASH_MAP( void*, VALUE_T, wxPointerHash, wxPointerEqual, \
-                          CLASSNAME, DECL )
+                          CLASSNAME, class )
 
 #define WX_DECLARE_EXPORTED_VOIDPTR_HASH_MAP( VALUE_T, CLASSNAME ) \
     WX_DECLARE_VOIDPTR_HASH_MAP_WITH_DECL( VALUE_T, CLASSNAME, \