[NativeAOT] Handle event pipe environment variable configuration and output to file

[elinor-fung]

Updates to NativeAOT event pipe:

• Respect environment variable configuration
• Handle writing out to a file
• Enable tracing/eventpipe/config/name_config_with_pid test, which uses environment variable configuration to write directly to a file.

Also some tweaks to headers to reduce some of the assumptions they have about what is/isn't included already.

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Issue Details

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Updates to NativeAOT event pipe:

• Respect environment variable configuration
• Handle writing out to a file for Windows - the TODO remains for non-Windows
• Enable tracing/eventpipe/config/name_config_with_pid test, which uses environment variable configuration to write directly to a file.

Also some tweaks to headers to reduce some of the assumptions they have about what is/isn't included already.

Author:	elinor-fung
Assignees:	-
Labels:	area-NativeAOT-coreclr
Milestone:	-

[elinor-fung]

Verified that the newly enabled test is running/passing in CI.
name_config_with_pid result: log
PayloadGroup0 now has three tracing tests enabled: log

[LakshanF]

LGTM, thanks for adding both environment variable and file support on all platforms!