Refactor to allow disabling features according to pg version

[Steve Chavez]

Problem

Right now the different modules logic are tangled per statement and the standard hook (run_process_utility_hook) is scattered everywhere. This makes it harder to maintain the code and to disable modules according to the pg version (#78, #50 (comment)).

static void
supautils_hook(PROCESS_UTILITY_PARAMS)
{
	Node   *utility_stmt = pstmt->utilityStmt;

	switch (utility_stmt->type)
	{
     		case T_AlterRoleStmt:
                  // privileged role logic..
                  // reserved role logic..   
                case T_CreateExtensionStmt:
                 // constrained extensions logic..
                 // privileged extensions logic..

Solution

Refactor the codebase so each module has a single entrypoint and the standard hook is invoked in one single place. Basically:

static void
supautils_hook(PROCESS_UTILITY_PARAMS)
{
  Node   *utility_stmt = pstmt->utilityStmt;
  ret1 = privileged_role_setup(utility_stmt)
  ret2 = reserved_roles_setup(utility_stmt)
  ret3 = privileged_extensions_setup(utility_stmt)
  ret4 = constrained_extensions_setup(utility_stmt)
  
  run_process_utility_hook(prev_hook);

  cleanup(ret1, ret2, ret3, ret4); // or have multiple cleanups depending on the module