Similar with #1751.

## Changes

Refactored `MessageEvent` initialization to use the builder pattern:

```java
new MessageEvent.Builder(...).build()
```

This prevents build failures when new fields are added to the
`MessageEvent` class.

Similar with #1751 and
#1761

## Changes

Refactored `XxxMessageContent` initialization to use the builder
pattern:

```java
new XxxMessageContent.Builder(...).build()
```

This prevents build failures when new fields are added to the
`XxxMessageContent` class.