fix: banners not properly destroyed

[dylancom]

Description

Added methods to clean up the banner when a bannerView unmounts.

Might fix #496?

Please test.

[docs-page[bot]]

To view this pull requests documentation preview, visit the following URL:

docs.page/invertase/react-native-google-mobile-ads~508

Documentation is deployed and generated using docs.page.

[codecov[bot]]

Codecov Report

Merging #508 (bf0ebd2) into main (79468a7) will decrease coverage by 0.41%. Report is 9 commits behind head on main. The diff coverage is n/a.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #508 +/- ## ========================================== - Coverage 44.16% 43.74% -0.41% ========================================== Files 29 29 Lines 530 535 +5 Branches 147 148 +1 ========================================== Hits 234 234 - Misses 296 301 +5 ```

[mikehardy]

:tada: This PR is included in version 12.7.1 :tada:

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

Your semantic-release bot :package::rocket: