Bokeh blur cache optimization

[Sergio0694]

Prerequisites

• I have written a descriptive pull-request title
• I have verified that there are no overlapping pull-requests open
• I have verified that I am following matches the existing coding patterns and practice as demonstrated in the repository. These follow strict Stylecop rules 👮.
• I have provided test coverage for my change (where applicable)

Description

The previous implementation of the BokehBlurProcessor<TPixel> was using a static ConcurrentDictionary<BokehBlurParameters, BokehBlurKernelData> field to store the preprocessed bokeh blur kernels for a pair of input parameters. The issue was that that static field was inside a generic class, meaning each concrete <TPixel> instantiation would've seen a completely different dictionary. As a result, running the same bokeh blur effect on multiple images of different pixel formats, even with the same parameters, would've caused the kernels to be recomputed every time, and stored separately in each dictionary, despite the kernels actually being exactly the same (they're not dependent on the pixel type they'll be used on).

This PR moves all the kernel preprocessing logic into a separate non-generic class, to solve the issues described above. I've also removed some unnecessary fields from the BokehBlurProcessor<TPixel> class, so that should also save a few bytes every time a new processor instance is created. 🚀

[codecov]

Codecov Report

Merging #1113 into master will increase coverage by 0.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #1113      +/-   ##
==========================================
+ Coverage      82%   82.02%   +0.01%     
==========================================
  Files         700      701       +1     
  Lines       28797    28797              
  Branches     3281     3281              
==========================================
+ Hits        23616    23621       +5     
+ Misses       4498     4494       -4     
+ Partials      683      682       -1

Flag	Coverage Δ
#unittests	82.02% <100%> (+0.01%)	⬆️

Impacted Files	Coverage Δ
...sors/Convolution/Parameters/BokehBlurKernelData.cs	100% <ø> (ø)	⬆️
...volution/Parameters/BokehBlurKernelDataProvider.cs	100% <100%> (ø)
...ocessors/Convolution/BokehBlurProcessor{TPixel}.cs	99.03% <100%> (+1.96%)	⬆️

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