83x speed up `resolveImportLocation`

[WebFreak001]

• adds windows & posix specific file/dir checks with existence, drops previous try-catch based code which improves performance in debug mode like x50 for the resolveImportLocation function
• exact .d matches inside import paths now immediately return on the first import path instead of returning at the end of the function being equal to the path inside the last matching import path
• file import paths no longer perform any IO if the path wouldn't match anyway
• remove array allocations for alternatives, now uses simpler code which can also return early

This gives a big speed up improvement in DCD on Windows:

Duration of first completion (ms)

	Old (Debug)	New (Debug)	Old (Release)	New (Release)
	457792	5600	98314	3878
	457994	5463	97429	3756
		5471	98454	3805
average	457893	5511	98066	3813
relative speed	100%	8308%	100%	2572%

Duration of later completions (ms)

	Old (Debug)	New (Debug)	Old (Release)	New (Release)
	177	66	163	61
	190	62	172	46
	192	61	155	67
average	186	63	163	58
relative speed	100%	296%	100%	282%

LDC 1.19.0 Target: x86_64-pc-windows-msvc Host CPU: ivybridge very little available RAM (<500 MB) some SSD

[WebFreak001]

Linux timings

note: these are also on a much more powerful machine, but I believe most speed reduction between OSs comes from fewer system wide import paths

Duration of first completion (ms)

	Old (Debug)	New (Debug)	Old (Release)	New (Release)
	10525	3306	9673	1516
	10518	3268	9839	1525
	10468	3261	9636	1552
average	10504	3278	9716	1531
relative speed	100%	320%	100%	635%

Duration of later completions (ms)

	Old (Debug)	New (Debug)	Old (Release)	New (Release)
	84	20	93	7
	116	23	91	11
	85	23	91	11
average	95	22	92	10
relative speed	100%	432%	100%	948%

LDC 1.22.0 Target: x86_64-pc-linux-gnu Host CPU: znver1 lots of available RAM fast NVMe SSD

[WebFreak001]

I would make a patch release to be compatible with the other newly released dsymbol for practical reasons now:

• the previous release is barely used as I released it 20h ago, making upgrades seamless
• the only breaking change from this is that multiple files with the same module name / suffix multiple import paths now use the first matching import path instead of the last matching import path
  • e.g. import foo.bar with matching import paths containing ["a/foo/bar.d", "b/foo/bar.d", "c/foo/bar.d"] would return
  • before: c/foo/bar.d
  • after: a/foo/bar.d