Throw better exceptions when invalid actor interfaces are used.

[philliphoff]

Description

Verifies that actor interfaces used to create actor proxies actually:

• Inherit from IActor
• Are publicly-visible

When interfaces are used that do not meet those requirements, a less cryptic error message is generated.

Issue reference

We strive to have all PR being opened based on an issue, where the problem or feature have been discussed prior to implementation.

Please reference the issue this PR will close: #859

Checklist

Please make sure you've completed the relevant tasks for this PR, out of the following list:

• Code compiles correctly
• Created/updated tests
• Extended the documentation

[codecov]

Codecov Report

Attention: 2 lines in your changes are missing coverage. Please review.

Comparison is base (10ef818) 66.53% compared to head (fb016d0) 66.52%.

Files	Patch %	Lines
src/Dapr.Actors/Client/ActorProxyFactory.cs	50.00%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1148      +/-   ##
==========================================
- Coverage   66.53%   66.52%   -0.02%     
==========================================
  Files         171      171              
  Lines        5752     5756       +4     
  Branches      626      628       +2     
==========================================
+ Hits         3827     3829       +2     
- Misses       1776     1777       +1     
- Partials      149      150       +1     

Flag	Coverage Δ
net6	66.51% <50.00%> (-0.02%)	⬇️
net7	66.51% <50.00%> (-0.02%)	⬇️
net8	66.51% <50.00%> (-0.02%)	⬇️

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