MAIN_PACKAGE string differs from package

https://github.com/google/mobly-snippet-lib/blame/9cb6d9e93baa6d4e0b8a650126a1fa3ef4c9810e/examples/ex4_uiautomator/src/main/java/com/google/android/mobly/snippet/example4/UiAutomatorSnippet.java#L49-L50

```
package com.google.android.mobly.snippet.example4;

...
private static final String MAIN_PACKAGE = "com.google.android.mobly.snippet.example2";
```

Could a comment be added for why the `MAIN_PACKAGE` is different from the package? Does this code actually work??

Start with examples/ex4_uiautomator/src/main/java/com/google/android/mobly/snippet/example4/UiAutomatorSnippet.java at the referenced MAIN_PACKAGE declaration and compare it with the package declaration. Trace how MAIN_PACKAGE is used to determine whether the mismatch is intentional or broken. Done means the behavior is explained and the code includes a clarifying comment or the discrepancy is corrected.

Written by the indexing model from the issue text.