Refactor distribution and extend tests for sub-distributions

[rasolca]

This PR consists of

• util_distribution.h
  • [x] refactoring
  • [x] extend tests with offsets
    • [x] fix a couple of bugs when using offsets
• distribution.h
  • [x] refactoring
  • [x] extract specific methods to distribution_extensions.h (internal methods)
  • [x] create aliases with the old names (which can be deprecated)
  • [x] extend tests
  • [x] fix bugs (Note: some bugs already fixed but not tested.)
  • [x] implement new methods needed for the distributed tridiagonal solver in distribution_extensions.h

[rasolca]

It's a bit hard to follow the changes because of the renamings, but from what I can tell it looks all valid. Thanks for spotting these issues!

I only have a few higher level comments at this point.

Sorry, the first review was only meant to check if the new interface made sense.

[rasolca]

cscs-ci run

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cscs-ci run

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cscs-ci run

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cscs-ci run

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[codecov-commenter]

Codecov Report

Merging #976 (bcb580a) into master (52704e9) will increase coverage by 0.16%. Report is 28 commits behind head on master. The diff coverage is 94.18%.

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@@            Coverage Diff             @@
##           master     #976      +/-   ##
==========================================
+ Coverage   93.42%   93.59%   +0.16%     
==========================================
  Files         143      144       +1     
  Lines        8686     8852     +166     
  Branches     1118     1119       +1     
==========================================
+ Hits         8115     8285     +170     
+ Misses        383      374       -9     
- Partials      188      193       +5     

Files	Coverage Δ
include/dlaf/matrix/layout_info.h	97.61% <100.00%> (ø)
include/dlaf/matrix/util_distribution.h	80.00% <100.00%> (-0.27%)	:arrow_down:
src/matrix/distribution.cpp	98.95% <100.00%> (+3.63%)	:arrow_up:
include/dlaf/matrix/distribution.h	93.26% <95.05%> (+4.64%)	:arrow_up:
include/dlaf/matrix/distribution_extensions.h	88.88% <88.88%> (ø)

... and 6 files with indirect coverage changes

[rasolca]

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