This mostly adds /** @var */ comments where they were missing, but a few
static array variables are converted into constants (presumably, array
constants were not yet supported when that code was written; they’re
supported since PHP 5.6), and a handful of unused variables are removed.

Also, add strict types to a lot of affected classes while we’re already
touching them, and remove method phpdoc comments if that makes them
redundant (i.e. ones that only contained type information).

Bug: T268827
Change-Id: Ib69a438d92a35913a9801199ad9492d412d00abc