[xkykai]

Closes #6237. Fixes the docs build, which has failed since #6228 in examples/global_wind_driven_gyres.jl: argmin of a field on a GPU TripolarGrid failed to compile (InvalidIRError, jl_f_throw_methoderror).

size(::AbstractField) uses indices(f), but operations adapted for a kernel see their fields' indices as nothing, so axes → size inside the broadcast kernel of findmin/findmax indexed nothing. size now falls back to the full axes through axes_indices, as axes already does.

grid = TripolarGrid(GPU(); size = (8, 10, 1), z = (0, 1))
c = Field{Center, Center, Nothing}(grid)
set!(c, (λ, φ) -> φ)
argmin(c) # InvalidIRError on main

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[xkykai]

close as duplicate of #6238!