xfs: pass perag references around when possible [v24.5]

Avoid the cost of perag radix tree lookups by passing around active perag
references when possible.

v24.2: rework some of the naming and whatnot so there's less opencoding

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
-----BEGIN PGP SIGNATURE-----

iHUEABYKAB0WIQQ2qTKExjcn+O1o2YRKO3ySh0YRpgUCZDdPZwAKCRBKO3ySh0YR
piV8AP910kUGZY23KEYp9FIHC2IbCqoK3XxNAOPD9vgEe42e5wD/d7KtMte3mXMp
cbsvjBYAC5JfjQ1235gTIEvZzDy/uQ4=
=H7Ct
-----END PGP SIGNATURE-----