non-visible-tiles-optimization for multi-tile-composition

[ptahmose]

Description

• Optimization of the tile-composition: before loading relevant subblocks, the tiles are checked whether they are visible (or whether they are completely overdrawn).
• This optimization is implemented for the ISingleChannelTileAccessor and ISingleChannelScalingTileAccessor. Although this optimization is expected to give exact same results (as before/without optimization enabled) and there should be no reason for not enabling it, it can be enabled/disabled with the corresponding options-structure. It is disabled by default currently.
• Fixed bug in CBitmapOperations::Fill_Gray8.

Fixes #75

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

• extensive unittests for the optimization are provided with the PR

Checklist:

• I followed the Contributing Guidelines.
• I did a self-review.
• I commented my code, particularly in hard-to-understand areas.
• I updated the documentation.
• I updated the version of libCZI following Versioning of libCZI depending on the type of change
  • Bug fix -> PATCH
  • New feature -> MINOR
  • Breaking change -> MAJOR
• I have added tests that prove my fix is effective or that my feature works.
• New and existing unit tests pass locally with my changes.

[ptahmose]

I put the PR in draft state again, I want to rework it a bit.