Add public Encoding.TryGetBytes/Chars

[stephentoub]

Fixes #84425

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Issue Details

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Fixes #84425

Author:	stephentoub
Assignees:	-
Labels:	area-System.Text.Encoding, new-api-needs-documentation
Milestone:	-

[stephentoub]

@EgorBo, fyi

[EgorBo]

@EgorBo, fyi

I've almost finished it but I'll wait for this PR to land and ideally a daily SDK to pick it up for easier testing/benchmarking if you don't mind 🙂

PS: if we could put this API into Utf8 class it would be easier for JIT but should work as is too. There is a small problem in JIT that it never inlines methods Encoding.UTF8.X without PGO (#85209)

[stephentoub]

There is a small problem in JIT that it never inlines methods Encoding.UTF8.X without PGO (#85209)

😦

"small problem"... so... fixable?

[EgorBo]

There is a small problem in JIT that it never inlines methods Encoding.UTF8.X without PGO (#85209)

😦

"small problem"... so... fixable?

We discussed some solutions, in the worst case we'll just intrinsify Encoding.UTF8 to return exact type right in the importer. But a proper fix will be better since many other use cases will benefit from it. My initial impl needs PGO being enabled but I'll land a workaround after it