fix(ec2): deprecated SubnetType enums are treated incorrectly (#21140)

In #19320, we changed the values of deprecated enums to include a `Deprecated_` prefix. This also meant we had to do some gymnastics in the code to change usages of the value to a switch case. 

However, there were also places in the code that do enum comparison, which uses the enum value. Those comparison points need to also explicitly consider the equivalent deprecated enums.  

Fixes #21131, Fixes #21138 

----

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packages/@aws-cdk/aws-ec2/lib/vpc.ts

@@ -1368,7 +1368,7 @@ export class Vpc extends VpcBase {
     this.createSubnets();
 
     const allowOutbound = this.subnetConfiguration.filter(
-      subnet => (subnet.subnetType !== SubnetType.PRIVATE_ISOLATED)).length > 0;
+      subnet => (subnet.subnetType !== SubnetType.PRIVATE_ISOLATED && subnet.subnetType !== SubnetType.ISOLATED)).length > 0;
 
     // Create an Internet Gateway and attach it if necessary
     if (allowOutbound) {
@@ -2205,7 +2205,8 @@ class ImportedSubnet extends Resource implements ISubnet, IPublicSubnet, IPrivat
  * They seem pointless but I see no reason to prevent it.
  */
 function determineNatGatewayCount(requestedCount: number | undefined, subnetConfig: SubnetConfiguration[], azCount: number) {
-  const hasPrivateSubnets = subnetConfig.some(c => c.subnetType === SubnetType.PRIVATE_WITH_NAT && !c.reserved);
+  const hasPrivateSubnets = subnetConfig.some(c => (c.subnetType === SubnetType.PRIVATE_WITH_NAT
+    || c.subnetType === SubnetType.PRIVATE) && !c.reserved);
   const hasPublicSubnets = subnetConfig.some(c => c.subnetType === SubnetType.PUBLIC);
 
   const count = requestedCount !== undefined ? Math.min(requestedCount, azCount) : (hasPrivateSubnets ? azCount : 0);

packages/@aws-cdk/aws-ec2/test/vpc.test.ts

@@ -30,6 +30,73 @@ import {
 
 describe('vpc', () => {
   describe('When creating a VPC', () => {
+
+    test('SubnetType.PRIVATE is equivalent to SubnetType.PRIVATE_WITH_NAT', () => {
+
+      const stack1 = getTestStack();
+      const stack2 = getTestStack();
+      new Vpc(stack1, 'TheVPC', {
+        subnetConfiguration: [
+          {
+            subnetType: SubnetType.PRIVATE,
+            name: 'subnet',
+          },
+          {
+            subnetType: SubnetType.PUBLIC,
+            name: 'public',
+          },
+        ],
+      });
+
+      new Vpc(stack2, 'TheVPC', {
+        subnetConfiguration: [
+          {
+            subnetType: SubnetType.PRIVATE_WITH_NAT,
+            name: 'subnet',
+          },
+          {
+            subnetType: SubnetType.PUBLIC,
+            name: 'public',
+          },
+        ],
+      });
+
+      const t1 = Template.fromStack(stack1);
+      const t2 = Template.fromStack(stack2);
+
+      expect(t1.toJSON()).toEqual(t2.toJSON());
+
+    });
+
+    test('SubnetType.ISOLATED is equivalent to SubnetType.PRIVATE_ISOLATED', () => {
+
+      const stack1 = getTestStack();
+      const stack2 = getTestStack();
+      new Vpc(stack1, 'TheVPC', {
+        subnetConfiguration: [
+          {
+            subnetType: SubnetType.ISOLATED,
+            name: 'subnet',
+          },
+        ],
+      });
+
+      new Vpc(stack2, 'TheVPC', {
+        subnetConfiguration: [
+          {
+            subnetType: SubnetType.PRIVATE_ISOLATED,
+            name: 'subnet',
+          },
+        ],
+      });
+
+      const t1 = Template.fromStack(stack1);
+      const t2 = Template.fromStack(stack2);
+
+      expect(t1.toJSON()).toEqual(t2.toJSON());
+
+    });
+
     describe('with the default CIDR range', () => {
 
       test('vpc.vpcId returns a token to the VPC ID', () => {