LibJS: Inline fast case for Value::to_{boolean,number,numeric,primitive}

These functions all have a very common case that can be dealt with a
very simple inline check, often avoiding the need to call an out-of-line
function. This patch moves the common case to inline functions in a new
ValueInlines.h header (necessary due to header dependency issues..)

8% speed-up on the entire Kraken benchmark :^)

Userland/Libraries/LibWeb/HTML/CustomElements/CustomElementRegistry.cpp

@@ -6,6 +6,7 @@
 
 #include <LibJS/Runtime/FunctionObject.h>
 #include <LibJS/Runtime/Iterator.h>
+#include <LibJS/Runtime/ValueInlines.h>
 #include <LibWeb/Bindings/CustomElementRegistryPrototype.h>
 #include <LibWeb/DOM/Document.h>
 #include <LibWeb/DOM/ElementFactory.h>