LibWebView: Do floating-point-error-free zoom calculation using rounding

The current min/max zoom levels are supposed to be: 30% and 500%.
Before, due to floating point error accumulation in incremental addition
of zoom-step into zoom-level, one extra zoom step would get allowed,
enabling user to zoom 20%-to-510%.

Now, using rounding, the intermediate zoom-level values should be as
close to the theoretical value as FP32 can represent. E.g. zoom-level of
70% (theoretical multiplier 0.7) is 0.69... .

Userland/Libraries/LibWebView/ViewImplementation.cpp

@@ -107,15 +107,15 @@ void ViewImplementation::zoom_in()
 {
     if (m_zoom_level >= ZOOM_MAX_LEVEL)
         return;
-    m_zoom_level += ZOOM_STEP;
+    m_zoom_level = round_to<int>((m_zoom_level + ZOOM_STEP) * 100) / 100.0f;
     update_zoom();
 }
 
 void ViewImplementation::zoom_out()
 {
     if (m_zoom_level <= ZOOM_MIN_LEVEL)
         return;
-    m_zoom_level -= ZOOM_STEP;
+    m_zoom_level = round_to<int>((m_zoom_level - ZOOM_STEP) * 100) / 100.0f;
     update_zoom();
 }