Kernel+LibELF: Don't blindly trust ELF symbol offsets in symbolication

It was possible to craft a custom ELF executable that when symbolicated
would cause the kernel to read from user-controlled addresses anywhere
in memory. You could then fetch this memory via /proc/PID/stack

We fix this by making ELFImage hand out StringView rather than raw
const char* for symbol names. In case a symbol offset is outside the
ELF image, you get a null StringView. :^)

Test: Kernel/elf-symbolication-kernel-read-exploit.cpp

Libraries/LibELF/ELFLoader.h

@@ -51,7 +51,7 @@ private:
 
     struct SortedSymbol {
         u32 address;
-        const char* name;
+        StringView name;
     };
 #ifdef KERNEL
     mutable OwnPtr<Region> m_sorted_symbols_region;