AK: Disable Vector insert/empend/prepend + a append overload in Kernel

We have whittled away at the usages of these AK::Vector APIs in the
Kernel. This change disables them from being visible when building
the Kernel to make sure no new usages get added.

AK/Vector.h

@@ -202,6 +202,8 @@ public:
         return false;
     }
 
+#ifndef KERNEL
+
     template<typename U = T>
     void insert(size_t index, U&& value) requires(CanBePlacedInsideVector<U>)
     {
@@ -224,6 +226,8 @@ public:
         MUST(try_extend(other));
     }
 
+#endif
+
     ALWAYS_INLINE void append(T&& value)
     {
         if constexpr (contains_reference)
@@ -237,10 +241,12 @@ public:
         MUST(try_append(T(value)));
     }
 
+#ifndef KERNEL
     void append(StorageType const* values, size_t count)
     {
         MUST(try_append(values, count));
     }
+#endif
 
     template<typename U = T>
     ALWAYS_INLINE void unchecked_append(U&& value) requires(CanBePlacedInsideVector<U>)
@@ -262,6 +268,7 @@ public:
         m_size += count;
     }
 
+#ifndef KERNEL
     template<class... Args>
     void empend(Args&&... args) requires(!contains_reference)
     {
@@ -284,6 +291,8 @@ public:
         MUST(try_prepend(values, count));
     }
 
+#endif
+
     // FIXME: What about assigning from a vector with lower inline capacity?
     Vector& operator=(Vector&& other)
     {