refactor: remove some small compile-time cycles

[thecristen]

No ticket, just trying to help our compile-time mess.

The current output of mix xref graph --format cycles --label compile-connected includes 5 distinct cycles.

This PR removes these 3 cycles:

Cycle of length 4 (2 compile):

    lib/dotcom/cldr.ex (compile)
    lib/dotcom/gettext.ex (compile)
    lib/dotcom/gettext/plural.ex
    lib/dotcom/locales.ex

Cycle of length 3 (2 compile):

    lib/dotcom/cache/multilevel.ex (compile)
    lib/dotcom/cache/publisher.ex
    lib/dotcom/cache/subscriber.ex (compile)

Cycle of length 2 (1 compile):

    lib/alerts/alert.ex
    lib/alerts/priority.ex (compile)

[joshlarson]

Left a few little nits, but I appreciate getting rid of a bunch of cycles!