Replace checkstyle with formatter to sort import

Historically, checkstyle was the only one respecting the android style
guide of sorting import.
Since an contribution in 2019, google-java-format does that properly:
https://github.com/google/google-java-format/pull/370/files

Note that checkstyle is now wrong for some import, as libcore is an
android import but checkstyle consider is as third party

The formatter is preferred as it will propose a fix command during the
hook

See style guide:
https://source.android.com/docs/setup/contribute/code-style#order-import-statements

Bug: 343776166
Test: None
Flag: Exempt INFRA
Change-Id: I3505cd15609e159413c0ea68fbcf25ae7c1e8e94