Logging Error object has a difficult to read output

### Related issues

### [REQUIRED] Version info

**node:** 10.22.0

**firebase-functions:** 3.11.0

**firebase-tools:** 8.9.0

**firebase-admin:** 8.13.0

### [REQUIRED] Test case

```
const firebaseFunctions = require('firebase-functions');
try {
throw new Error('Message from the thrown error.');
} catch (err) {
firebaseFunctions.logger.error('Logged message', err);
}
```

### [REQUIRED] Steps to reproduce

Run the test case. For example:

```
const firebaseFunctions = require('firebase-functions');

it('Test', () => {
try {
throw new Error('Message from the thrown error.');
} catch (err) {
firebaseFunctions.logger.error('Logged message', err);
}
});
```

### [REQUIRED] Expected behavior

Something like:
```
{
"severity":"ERROR",
"message":"Logged message"
"stack":"Error: Message from the thrown error.\n "
}
```

### [REQUIRED] Actual behavior

```
{
"severity":"ERROR",
"message":"Logged message Error: Message from the thrown error.\n "
}
```

### Were you able to successfully deploy your functions?

Yes, it deploys fine. This is about logging errors in a way that is easier to read.

The actual output isn't ideal because the the logged `message` ("Logged message ") is concatenated with the `Error` object's `message` ("Message from the thrown error.") and `stack`. It's clear this happens because Error isn't a simple object, which means the logger won't interpret it as a "jsonPayload". However, this makes reading errors more difficult. Is there a way to log errors so that the output is more like the following?

This is just the tip of the iceberg, because I'd like to create custom error `class`es that `extends` the `Error` class, but those print just as poorly.