port encryptFile to use PGPainless

[tomholub]

Part of #1051

Relevant test here https://github.com/FlowCrypt/flowcrypt-mobile-core/blob/master/source/test.ts#L53

Only port encryptFile for now (which results in binary - unarmored - output). Don't port decryptFile because there are many error scenarios that we want to behave the same as before.

for (const keypairName of allKeypairNames.filter(name => name != 'expired')) {
 ava.default(`encryptFile -> decryptFile ${keypairName}`, async t => {
 const { pubKeys, keys } = getKeypairs(keypairName);
 const name = 'myfile.txt';
 const content = Buffer.from([10, 20, 40, 80, 160, 0, 25, 50, 75, 100, 125, 150, 175, 200, 225, 250]);
 const { data: encryptedFile, json: encryptJson } = await request('encryptFile', { pubKeys, name }, content);
 expectEmptyJson(encryptJson);
 expectData(encryptedFile);
 const { data: decryptedContent, json: decryptJson } = await request('decryptFile', { keys }, encryptedFile);
 expect(decryptJson).to.deep.equal({ success: true, name });
 expectData(decryptedContent, 'binary', content);
 t.pass();
 });
}

Current implementation here https://github.com/FlowCrypt/flowcrypt-mobile-core/blob/master/source/mobile-interface/endpoints.ts

 public encryptFile = async (uncheckedReq: any, data: Buffers): Promise<Buffers> => {
 const req = ValidateInput.encryptFile(uncheckedReq);
 const encrypted = await PgpMsg.encrypt({ pubkeys: req.pubKeys, data: Buf.concat(data), filename: req.name, armor: false }) as OpenPGP.EncryptBinaryResult;
 return fmtRes({}, encrypted.message.packets.write());
 }