Order and filter processors by supported commands

[ronaldbarendse]

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Description

This fixes issue #182 by ordering and filtering the processors by supported commands.

The biggest change this introduces is not calling the Process(...) method on processors where the Commands collection doesn't contain a parsed command.

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[ronaldbarendse]

I just tested this PR again (with browser caching off) and noticed it always returned -1 as lowest index... Now it uses an intersection of parsed commands and commands supported by the processor, so it really gets the first index of a supported command 😄

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Because case sensitivity of the commands depend on the comparer used in the dictionary returned by ParseRequestCommands, I've made sure this is also used when stripping out unknown commands and getting the first index for processing. Previously when requesting /imagesharp-logo.png?WIDTH=300 (in Edge, as Chrome seems to be smart and remember the 'correct' URL casing), it stripped out the command, even though the ResizeWebProcessor would use the correct width/value.

It's probably also fine to always use StringComparer.OrdinalIgnoreCase, as that removes the need to get the comparer from the concrete dictionary type...

[JimBobSquarePants]

Thanks for the PR. I need to do a thorough review + perf check this but I've made some notes.

[codecov]

Codecov Report

Merging #183 (ab8eecb) into master (b11fe03) will decrease coverage by 0.05%.
The diff coverage is 94.44%.

@@            Coverage Diff             @@
##           master     #183      +/-   ##
==========================================
- Coverage   84.71%   84.65%   -0.06%     
==========================================
  Files          50       50              
  Lines        1426     1440      +14     
  Branches      190      194       +4     
==========================================
+ Hits         1208     1219      +11     
- Misses        164      166       +2     
- Partials       54       55       +1     

Flag	Coverage Δ
unittests	84.65% <94.44%> (-0.06%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
.../ImageSharp.Web/Middleware/ImageSharpMiddleware.cs	85.92% <0.00%> (ø)
...ageSharp.Web/Processors/WebProcessingExtensions.cs	100.00% <100.00%> (ø)
...p.Web/Middleware/ConcurrentDictionaryExtensions.cs	50.00% <0.00%> (-21.43%)	⬇️

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[JimBobSquarePants]

I think you're onto something here but I think we can reduce the workload.

[JimBobSquarePants]

Thanks for your help here @ronaldbarendse I'll get an official release out asap with these changes.