Use pathlib for path resolution

[ahopkins]

Piggyback off #2495 to use pathlib. This way we do not need to do any of the path calculations.

[codecov]

Codecov Report

Merging #2506 (d83229a) into main (2fa28f1) will decrease coverage by 0.042%.
The diff coverage is 83.333%.

@@              Coverage Diff              @@
##              main     #2506       +/-   ##
=============================================
- Coverage   87.434%   87.392%   -0.043%     
=============================================
  Files           69        69               
  Lines         5555      5560        +5     
  Branches       966       966               
=============================================
+ Hits          4857      4859        +2     
- Misses         507       509        +2     
- Partials       191       192        +1     

Impacted Files	Coverage Δ
sanic/mixins/routes.py	93.700% <83.333%> (+0.126%)	⬆️
sanic/server/protocols/http_protocol.py	81.617% <0.000%> (-2.206%)	⬇️

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[ahopkins]

Thanks @seemethere. Hope you've been well. 😎

@Tronic @ChihweiLHBird @prryplatypus I changed the pattern to use pathlib so that we can rely upon the stdlib for all the various path resolution Path().resolve(). Also, I think we need 404 for all of the exceptions. A 400 could leak information.

[ChihweiLHBird]

Migrate to pathlib is awesome!