Reduce lockscreen bottom area on small land screens - legacy support

See:
- ag/24656550 - Reduce lockscreen bottom area on small land screens
- this CL only 'adds support for the new lockscreen implementation'
- but this is currently also guarded by flags:
    - MIGRATE_SPLIT_KEYGUARD_BOTTOM_AREA (b/290652751)
    - MIGRATE_LOCK_ICON (b/290652751)

This CL 'adds support for the old implementation for lockscreen'

- lock icon moved downwards (reduced margins), and centred by including left + right insets when calculating midpoint (screen centre is used when UDFPS is not enabled)
- indication area moved downwards (reduced margins)

This is a required feature for landscape lockscreen for small screens

Guarded by flag "lockscreen.enable_landscape" (b/293252410)

Bug: 296571001
Bug: 293252410

Test: LockIconViewControllerTest
Change-Id: I97c1d21c13249a7e655098d44d331b5af4c41df7