cmake: Add missing dependency checks in package config

[stotko]

Up to now, dependencies in the package config file are not explicitly stated. Instead, there was the assumption that thrust is located always in the CUDA include directories which are implicitly handled. Although this approach worked until the introduction of the backend system (including an OpenMP backend) and the recent thrust detection cleanup (see #92), it is fundamentally broken now. Properly setup and handle the dependencies in the package config file to fix configuration errors on the user's side.

[codecov]

Codecov Report

Merging #94 into master will not change coverage by %.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #94   +/-   ##
=======================================
  Coverage   97.82%   97.82%           
=======================================
  Files          27       27           
  Lines        1611     1611           
=======================================
  Hits         1576     1576           
  Misses         35       35           

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