Make PacketList a valid subtype of Array and update Packet.tag types (#1289)

Changes:
- Implementation:
  - Remove `PacketList.prototype.concat` and `push`
    (we solely rely on `Array.push` instead)
  - Fix https://github.com/openpgpjs/openpgpjs/issues/907 by
    correctly handling result of `filterByTag`
  - Implement `write()` method for `Trust` and `Marker` packets,
    to make them compatible with the `BasePacket` interface
- Types:
  - Simplify and updated `PacketList` type definitions
  - Fix types for `Packet.tag`, which is `static` since
    https://github.com/openpgpjs/openpgpjs/pull/1268
  - Prevent passing SubkeyPackets where KeyPackets are expected,
    and vice versa

test/typescript/definitions.ts

@@ -6,9 +6,13 @@
  *  - if it fails to run, edit this file to match the actual library API, then edit the definitions file (openpgp.d.ts) accordingly.
  */
 
-import { generateKey, readKey, readKeys, Key, readMessage, createMessage, Message, createCleartextMessage, encrypt, decrypt, sign, verify, config } from '../..';
-
 import { expect } from 'chai';
+import {
+  generateKey, readKey, readKeys, Key,
+  readMessage, createMessage, Message, createCleartextMessage,
+  encrypt, decrypt, sign, verify, config, enums,
+  LiteralDataPacket, PacketList, CompressedDataPacket, PublicKeyPacket, PublicSubkeyPacket, SecretKeyPacket, SecretSubkeyPacket
+} from '../..';
 
 (async () => {
 
@@ -78,6 +82,34 @@ import { expect } from 'chai';
   const verifiedBinaryData: Uint8Array = verifiedBinary.data;
   expect(verifiedBinaryData).to.deep.equal(binary);
 
+  // Generic packetlist
+  const packets = new PacketList();
+  expect(packets.push()).to.equal(0);
+  expect(packets.push(new LiteralDataPacket())).to.equal(1);
+  packets.map(packet => packet.write);
+  // @ts-expect-error for unsafe downcasting
+  packets.map((packet: LiteralDataPacket) => packet.getText());
+  // @ts-expect-error for non-packet element
+  try { new PacketList().push(1); } catch (e) {}
+
+
+  // Packetlist of specific type
+  const literalPackets = new PacketList<LiteralDataPacket>();
+  literalPackets.push(new LiteralDataPacket());
+  literalPackets[0].write();
+  literalPackets.map((packet: LiteralDataPacket) => packet);
+  packets.push(...literalPackets);
+  // @ts-expect-error for incompatible packetlist type
+  literalPackets.push(...packets);
+  // @ts-expect-error for incompatible packet type
+  new PacketList<LiteralDataPacket>().push(new CompressedDataPacket());
+  // @ts-expect-error for incompatible packet type
+  new PacketList<PublicKeyPacket>().push(new PublicSubkeyPacket());
+  // @ts-expect-error for incompatible packet type
+  new PacketList<SecretKeyPacket>().push(new SecretSubkeyPacket());
+
+  expect(LiteralDataPacket.tag).to.equal(enums.packet.literalData);
+
   // // Detached - sign cleartext message (armored)
   // import { Message, sign } from 'openpgp';
   // const message = await createMessage({ text: util.removeTrailingSpaces(text) });