Create a simple framework for Hyde extensions

[caendesilva]

Adds a simple framework for creating Hyde extensions. I'm making this in parallel with #827. My initial thought was to house arrays of booting callbacks but I think those often makes it hard to understand where things are happening. This PR adds a base class that can be extended and registered. It's public methods are then called statically at the appropriate times, injecting any relevant dependencies.

Todo:

• Add tests
• Add documentation

[codecov]

Codecov Report

Merging #828 (be6f30b) into master (13f58e8) will not change coverage.
The diff coverage is 100.00%.

@@              Coverage Diff              @@
##              master      #828     +/-   ##
=============================================
  Coverage     100.00%   100.00%             
- Complexity      1193      2406   +1213     
=============================================
  Files            144       290    +146     
  Lines           3152      6342   +3190     
=============================================
+ Hits            3152      6342   +3190     

Impacted Files	Coverage Δ
packages/framework/src/Foundation/HydeKernel.php	100.00% <ø> (ø)
...ramework/src/Foundation/Concerns/HydeExtension.php	100.00% <100.00%> (ø)
...work/src/Foundation/Concerns/ManagesHydeKernel.php	100.00% <100.00%> (ø)
...ckages/framework/src/Foundation/FileCollection.php	100.00% <100.00%> (ø)
...ckages/framework/src/Foundation/PageCollection.php	100.00% <100.00%> (ø)
...kages/framework/src/Foundation/RouteCollection.php	100.00% <100.00%> (ø)
...work/src/Framework/Concerns/ValidatesExistence.php	100.00% <100.00%> (ø)
.../src/Framework/Concerns/RegistersFileLocations.php	100.00% <0.00%> (ø)
.../Framework/Features/Metadata/GlobalMetadataBag.php	100.00% <0.00%> (ø)
...p/packages/framework/src/Foundation/HydeKernel.php	100.00% <0.00%> (ø)
... and 142 more

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