LibELF: Use binary search when looking up symbols :^)

For whatever reason, symbolication was doing an O(n) walk of all the
symbols, despite having sorted them beforehand.

Changing this to a binary_search() makes symbolication noticeably
faster and improves Profiler startup time.

Userland/Libraries/LibELF/Image.h

@@ -216,6 +216,9 @@ private:
         Optional<Image::Symbol> symbol;
     };
 
+    void sort_symbols() const;
+    SortedSymbol* find_sorted_symbol(FlatPtr) const;
+
     mutable Vector<SortedSymbol> m_sorted_symbols;
 };