LibCrypto: Make `PEMType` an enum class

This is required for the following commits to avoid a conflict
with the `Certificate` namespace.

Libraries/LibCrypto/ASN1/PEM.cpp

@@ -100,11 +100,11 @@ ErrorOr<ByteBuffer> encode_pem(ReadonlyBytes data, PEMType type)
     StringView block_end;
 
     switch (type) {
-    case Certificate:
+    case PEMType::Certificate:
         block_start = "-----BEGIN CERTIFICATE-----\n"sv;
         block_end = "-----END CERTIFICATE-----\n"sv;
         break;
-    case PrivateKey:
+    case PEMType::PrivateKey:
         block_start = "-----BEGIN PRIVATE KEY-----\n"sv;
         block_end = "-----END PRIVATE KEY-----\n"sv;
         break;

Libraries/LibCrypto/ASN1/PEM.h

@@ -11,7 +11,7 @@
 
 namespace Crypto {
 
-enum PEMType {
+enum class PEMType {
     Certificate,
     PrivateKey,
 };