LibWeb: Add a TimingFunction struct implementing the Web Easing spec

This is mostly a copy-paste of the algorithms already in StyleComputer
with spec links and comments. The only thing that really changed is the
handling of values outside of the range [0, 1] in the cubic bezier
function.

The implementation in StyleComputer will be removed in a later commit.

Userland/Libraries/LibWeb/CMakeLists.txt

@@ -6,6 +6,7 @@ set(SOURCES
     Animations/AnimationEffect.cpp
     Animations/AnimationTimeline.cpp
     Animations/DocumentTimeline.cpp
+    Animations/TimingFunction.cpp
     ARIA/AriaData.cpp
     ARIA/ARIAMixin.cpp
     ARIA/Roles.cpp