doc: add documentation for FindMangledFunctionName

Author: Nerixyz

lldb/source/Plugins/SymbolFile/NativePDB/SymbolFileNativePDB.h

@@ -140,6 +140,10 @@ class SymbolFileNativePDB : public SymbolFileCommon {
 
   std::optional<PdbCompilandSymId> FindSymbolScope(PdbCompilandSymId id);
 
+  /// Find the mangled name for a function
+  ///
+  /// \param id A symbol ID of a S_LPROC32/S_GPROC32 record
+  /// \returns The mangled name of the function (if available)
   std::optional<llvm::StringRef> FindMangledFunctionName(PdbCompilandSymId id);
 
   void FindTypes(const lldb_private::TypeQuery &match,