C++: Complete support for char8_t

cpp/ql/src/semmle/code/cpp/Type.qll

@@ -465,6 +465,8 @@ private predicate integralTypeMapping(int original, int canonical, int unsigned,
   original = 43 and canonical = 43 and unsigned = -1 and signed = -1 // char16_t
   or
   original = 44 and canonical = 44 and unsigned = -1 and signed = -1 // char32_t
+  or
+  original = 51 and canonical = 51 and unsigned = -1 and signed = -1 // char8_t
 }
 
 /**

cpp/ql/src/semmle/code/cpp/padding/Padding.qll

@@ -157,6 +157,8 @@ abstract class Architecture extends string {
     or
     t instanceof WideCharType and result = wideCharSize()
     or
+    t instanceof Char8Type and result = 8
+    or
     t instanceof Char16Type and result = 16
     or
     t instanceof Char32Type and result = 32