CI: enable pedantic for each cabal package separately

[jhrcek]

It seems that the original "all +pedantic" doesn't enable pedantic flag for everything
If you run cabal configure --constraint "all +pedantic" followed by

cabal build -v2   #among other things verbosity level 2 outputs "Flags chosen: ... pedantic=False... " for each target
# or 
cabal build -v2 all
# or 
cabal build -v2 <specific-component>

you' won't see any pedantic=True anywhere.
Doing it on per-cabal-file basis seems to work fine (and leads to desirable CI failures).

[michaelpj]

Baffling.

[jhrcek]

Closing this for now as I enabled pedantic for most subprojects in #4224
Will work towards fixing all warnings in ghcide in separate PR.