Debugger: Add support for two more floating point display formats

1. The `std::hexfloat` representation produced by `std::sstream`.
2. Breaking the number into a normalized value and a integral power of 2,
   as does the `std::frexp()` function.

M_PI looks like "0x1.921fb54442d18p+1" and "0.785398163397 * 2^2"
respectively.

Fixes: QTCREATORBUG-26793
Change-Id: Ib08ea9408f79201434eb75ec328b94ab933259a4
Reviewed-by: Leena Miettinen <riitta-leena.miettinen@qt.io>
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

src/plugins/debugger/watchdata.cpp

@@ -628,6 +628,19 @@ QString WatchItem::sourceExpression() const
     return QString("%1.%2").arg(p->sourceExpression(), name);
 }
 
+int WatchItem::guessSize() const
+{
+    if (size != 0)
+        return size;
+    if (type == "double")
+        return 8;
+    if (type == "float")
+        return 4;
+    if (type == "qfloat16")
+        return 2;
+    return 0;
+}
+
 } // namespace Internal
 } // namespace Debugger