interfaces, o/ifacestate: don't allow devmode snaps calling other snaps on UC22

[anonymouse64]

Eventually we will also disable this behavior of being able to call snap-confine from a devmode snap for all other systems, but for now we can only get away with disabling UC22.

Also add missing unit tests from the branch we didn't have time to write/prepare.

[codecov-commenter]

Codecov Report

Merging #11408 (3a3e11f) into master (f0ff569) will increase coverage by 0.02%. The diff coverage is 50.00%.

@@            Coverage Diff             @@
##           master   #11408      +/-   ##
==========================================
+ Coverage   78.34%   78.37%   +0.02%     
==========================================
  Files         931      931              
  Lines      107005   107023      +18     
==========================================
+ Hits        83838    83881      +43     
+ Misses      17951    17924      -27     
- Partials     5216     5218       +2     

Flag	Coverage Δ
unittests	78.37% <50.00%> (+0.02%)	:arrow_up:

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
interfaces/ifacetest/backendtest.go	0.00% <0.00%> (ø)
overlord/ifacestate/helpers.go	76.07% <33.33%> (-0.46%)	:arrow_down:
interfaces/apparmor/backend.go	84.37% <100.00%> (+6.36%)	:arrow_up:
overlord/hookstate/hookmgr.go	74.67% <0.00%> (-0.65%)	:arrow_down:
overlord/ifacestate/handlers.go	64.87% <0.00%> (-0.15%)	:arrow_down:
daemon/api_connections.go	93.58% <0.00%> (+0.53%)	:arrow_up:

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[anonymouse64]

I will split off the other unit tests into a separate PR, I was probably too self-confident in thinking the model stuff would not be complex

[anonymouse64]

Other unit tests split out into https://github.com/snapcore/snapd/pull/11409

[ernestl]

@pedronis do we want to pursue this any further?

[pedronis]

@pedronis do we want to pursue this any further?

yes, this and a related problem are on my/our tech debt list. Finding time/timing time is complicated though