fix(android): remove unchecked Java compilation warnings

## Summary

Compiling the Capacitor Android library with `-Xlint:unchecked` reports eight
unchecked operations in the current 8.4.1 release and on `main`.

## Reproduction

From an Android app that includes `@capacitor/android@8.4.1`, configure Java
compile tasks with `-Xlint:unchecked` and run:

```text
./gradlew :capacitor-android:clean :capacitor-android:compileReleaseJavaWithJavac --console=plain
```

The default compilation emits the generic `Some input files use unchecked or
unsafe operations` note.

## Affected source

- `android/capacitor/src/main/java/com/getcapacitor/Plugin.java:679` constructs
a raw `CopyOnWriteArrayList` from a `List`.
- `android/capacitor/src/main/java/com/getcapacitor/BridgeWebChromeClient.java`
stores the permission and activity launchers as raw `ActivityResultLauncher`
values, producing six unchecked calls at lines 120, 267, 298, 350, 369, and
401.

## Expected behavior

The released Android library should compile without unchecked-operation notes.
Parameterizing the collection construction and the two launcher fields should
remove the warnings without changing behavior.

Inspect android/capacitor/src/main/java/com/getcapacitor/Plugin.java around line 679 and BridgeWebChromeClient.java, focusing on the raw collection and ActivityResultLauncher fields identified in the issue. Run ./gradlew :capacitor-android:clean :capacitor-android:compileReleaseJavaWithJavac --console=plain with -Xlint:unchecked enabled; done means the Android library compiles without unchecked-operation warnings and behavior is unchanged.

Written by the indexing model from the issue text.