[release/6.0-rc1] Give tvOS a special value for Personal/MyDocuments

[directhex]

Backport of #57508 to release/6.0-rc1

/cc @directhex

Customer Impact

Fixes two issues where tvOS devices have read-only directories which are read-write on other Apple platforms; SpecialFolders.Personal (and subdirectories thereof), and TMP.

Testing

Manual testing on Helix & local device

Risk

Low - makes minor changes to how temp folders are calculated on all iOS-like targets, which should be more futureproof if Apple stops allowing /tmp or TMP in an OS update

Fixes#34007
Fixes#57638

Backport of #57508 to release/6.0-rc1

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Issue Details

---

Backport of #57508 to release/6.0-rc1

/cc @directhex

Customer Impact

Fixes two issues where tvOS devices have read-only directories which are read-write on other Apple platforms; SpecialFolders.Personal (and subdirectories thereof), and TMP.

Testing

Manual testing on Helix & local device (we don't CI on devices currently, and the issues are device-only)

Risk

Low - makes minor changes to how temp folders are calculated on all iOS-like targets, which should be more futureproof if Apple stops allowing /tmp or TMP in an OS update

Fixes #34007
Fixes #57638

Backport of #57508 to release/6.0-rc1

Author:	directhex
Assignees:	-
Labels:	Servicing-consider, area-System.Runtime
Milestone:	-

[Anipik]

approved offline

[directhex]

/backport to release/6.0

[github-actions]

Started backporting to release/6.0: https://github.com/dotnet/runtime/actions/runs/1175313005