[Base/GPU] Cleanup float comparisons and NaN and -0 in clamping

C++ relational operators are supposed to raise FE_INVALID if an argument is
NaN, use std::isless/greater[equal] instead where they were easy to locate
(though there are other places possibly, mostly min/max and clamp usage was
checked).

Also fixes a copy-paste error making the CPU shader interpreter execute
MINs as MAXs instead.

src/xenia/gpu/trace_viewer.cc

@@ -1066,7 +1066,7 @@ void ProgressBar(float frac, float width, float height = 0,
   if (height == 0) {
     height = ImGui::GetTextLineHeightWithSpacing();
   }
-  frac = xe::saturate_unsigned(frac);
+  frac = xe::saturate(frac);
 
   const auto fontAtlas = ImGui::GetIO().Fonts;