LibSymbolication: Make Symbol comparable

All its members are comparable themselves, so this can be defaulted.
Making it comparable will allow us, among other things, to check if a
list of symbols (i.e., the result of calling the symbolicate functions)
is equal or not to another, which in turn will allow us to avoid
refreshing the SystemMonitor's Stack tab when successive symbolicated
stacks are the same.

Userland/Libraries/LibSymbolication/Symbolication.h

@@ -17,6 +17,7 @@ struct Symbol {
     String object {};
     u32 offset { 0 };
     Vector<Debug::DebugInfo::SourcePosition> source_positions;
+    bool operator==(Symbol const&) const = default;
 };
 
 Optional<FlatPtr> kernel_base();