[SHELL32][SHELL32_APITEST][SDK] Implement ShellExec_RunDLL (#7615)

Implementing missing features...
JIRA issue: CORE-19278
- Modify shell32.spec.
- Move function definitions
  from stubs.cpp into shlexec.cpp.
- Add prototypes to <undocshell.h>.

sdk/include/reactos/undocshell.h

@@ -712,6 +712,27 @@ RealShellExecuteExW(
     _Out_opt_ PHANDLE lphProcess,
     _In_ DWORD dwFlags);
 
+VOID WINAPI
+ShellExec_RunDLL(
+    _In_opt_ HWND hwnd,
+    _In_opt_ HINSTANCE hInstance,
+    _In_ PCSTR pszCmdLine,
+    _In_ INT nCmdShow);
+
+VOID WINAPI
+ShellExec_RunDLLA(
+    _In_opt_ HWND hwnd,
+    _In_opt_ HINSTANCE hInstance,
+    _In_ PCSTR pszCmdLine,
+    _In_ INT nCmdShow);
+
+VOID WINAPI
+ShellExec_RunDLLW(
+    _In_opt_ HWND hwnd,
+    _In_opt_ HINSTANCE hInstance,
+    _In_ PCWSTR pszCmdLine,
+    _In_ INT nCmdShow);
+
 /* RegisterShellHook types */
 #define RSH_DEREGISTER        0
 #define RSH_REGISTER          1