P4Lang/Program/InstancesWithTypes and TypesWithTypes

Add helper functions to fetch globally instantiated/declared
parser/controls (etc) and types in a user's P4 program.

Signed-off-by: Will Hawkins <hawkinsw@obs.cr>

Snippets/use-program-instanceswithtypes.swift

@@ -0,0 +1,50 @@
+// p4rse, Copyright 2026, Will Hawkins
+//
+// This file is part of p4rse.
+//
+// This file is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program. If not, see <https://www.gnu.org/licenses/>.
+
+import Common
+import Foundation
+import Runtime
+import SwiftTreeSitter
+import Testing
+import TreeSitter
+import TreeSitterP4
+import P4Lang
+import P4Compiler
+
+let p4_program_with_control_decl = """
+  control simple() {
+    action a() {
+    }
+    table t {
+      key = {
+        true: exact;
+      }
+    }
+  };
+  """
+
+
+// snippet.include
+let flter = { (tipe: P4Type) -> Bool in
+  switch tipe {
+  case let c as Control: c.name == "simple"
+  default: false
+  }
+}
+if case .Ok(let program) = Program.Compile(p4_program_with_control_decl) {
+  print(program.InstancesWithTypes(flter))
+}