Optimize FontSourceCollection creation from a filesystem directory, reduce allocs

[h3xds1nz]

Description

Optimizes building of FontSourceCollection and also some work in FontResourceCache.

• Path.GetExtension has a span variant, this prevents string creation just to check IsSupportedFontExtension.
• SupportedExtensions static array has been removed as it is not needed for anything, anymore.
• I've included the code-path removal for isWindowsFonts from the previous PR, hence why this is a draft.
• Instead of using Directory.GetFiles, we will use the underlying implementation on .NET Core; the FileSystemEnumerable.
  • I've copied the enumeration options to mimic what Directory.GetFiles(string) does (Compatible).
  • We do not need the MatchType to be specified at all (which would be Win32), so it is not.
  • This will greatly reduce allocations when querying folders with unsupported files, etc.,
• In case of a single file://, we will no longer allocate a string[] of 1.

416 files in directory, no matches

Method	Mean [ns]	Error [ns]	StdDev [ns]	Gen0	Code Size [B]	Gen1	Allocated [B]
Original	147,452.0 ns	1,774.1 ns	1,659.5 ns	5.6152	4,449 B	1.2207	96320 B
PR__EDIT2	112,287.9 ns	534.4 ns	473.7 ns	-	5,824 B	-	368 B

351 files in directory, 156 matches

Method	Mean [ns]	Error [ns]	StdDev [ns]	Gen0	Code Size [B]	Gen1	Allocated [B]
Original	170,543.1 ns	973.2 ns	812.6 ns	3.6621	4,989 B	0.2441	62760 B
PR__EDIT2	153,370.2 ns	999.2 ns	885.7 ns	1.4648	4,539 B	-	25888 B

5 files, 1 match

Method	Mean [ns]	Error [ns]	StdDev [ns]	Gen0	Code Size [B]	Allocated [B]
Original	20,788.0 ns	143.1 ns	126.9 ns	0.0916	5,025 B	1768 B
PR__EDIT2	19,837.8 ns	161.6 ns	151.2 ns	0.0305	6,521 B	600 B

1 file, 1 match

Method	Mean [ns]	Error [ns]	StdDev [ns]	Gen0	Code Size [B]	Allocated [B]
Original	19,390.3 ns	177.1 ns	165.7 ns	0.0305	5,031 B	752 B
PR__EDIT2	19,281.6 ns	205.9 ns	189.4 ns	0.0305	6,525 B	600 B

Customer Impact

Decreased allocations, increased performance when initializing from directory.
I've observed about 3-4ms improvement when building from Fonts directory (351 files; 156 matches).

Regression

No.

Testing

Local build, initializing the collection with folders to look in, testing the functinality via FontFamily change.

Risk

Low, this is rather simple 1:1 swap. Options for FileSystemEnumerable were copied for GetFiles codepath.

Microsoft Reviewers: Open in CodeFlow

[h3xds1nz]

Resolved merge conflicts 11