perf: improve try_files matcher

[dunglas]

This is an experiment to use repl.Match() to (likely) prevent useless string manipulations.
This improve the performance of 2%, but consumes 10% more memory. I'm not sure if it is worth it. (the gain is likely a better on Windows)

Before:

goos: darwin
goarch: arm64
pkg: github.com/caddyserver/caddy/v2/modules/caddyhttp/fileserver
cpu: Apple M1 Pro
BenchmarkFileMatcher
BenchmarkFileMatcher-10    	   81501	     14692 ns/op	     920 B/op	      22 allocs/op
PASS

After:

goos: darwin
goarch: arm64
pkg: github.com/caddyserver/caddy/v2/modules/caddyhttp/fileserver
cpu: Apple M1 Pro
BenchmarkFileMatcher
BenchmarkFileMatcher-10    	   81658	     14410 ns/op	    1022 B/op	      20 allocs/op
PASS

[dunglas]

Likey useless.

[mholt]

This is kinda surprising to me, as it should only make allocations if invoked.

Maybe the benchmark is not representative of real life use?

[mholt]

Hmm no the benchmark looks fine 🤔

[dunglas]

Map() itself needs to allocate to keep the data available until it is called.

Here it is not worth it at least on Unix because ToSlash() basically does nothing on this OS.