[Feature Request] Make `AdManagerBannerAd` recyclable

[hellohuanlin]

From our customer: they want to recycle AdManagerBannerAd as well.

It should be similar change to flutter/flutter#158944 (hopefully)

[jmagman]

PR is #1275

[malandr2]

ACK. Assigning to @LTPhantom to implement.

[malandr2]

Closing as this was resolved in #1275

[jmagman]

@malandr2 I believe this is a separate request for AdManagerBannerAd specifically, which #1275 didn't address.

[hellohuanlin]

That's correct. @malandr2 could you re-open the issue (i don't have permission)

[malandr2]

Ah, understood. Re-opening!