Rename `RdXmlFile` to `_DirectivesFile`

[MichalStrehovsky]

To make it 100% visible this is an unsupported internal option that may change or disappear one day without a breaking change warning or anything.

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Issue Details

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To make it 100% visible this is an unsupported internal option that may change or disappear one day without a breaking change warning or anything.

Author:	MichalStrehovsky
Assignees:	-
Labels:	area-NativeAOT-coreclr
Milestone:	8.0.0

[wjk]

If you intend to make this API private, what are the supported alternatives?

[MichalStrehovsky]

If you intend to make this API private, what are the supported alternatives?

It only was "public" in the experimental repos as an experiment and even there it was generating a warning for years: dotnet/runtimelab#875. I don't think we would delete it anytime soon, but it's only meant for temporary workarounds. The real fix is the make the code AOT/trimming compatible and that's where all the guidelines are going to be. RdXmlFile didn't make it into docs.microsoft.com and the references to it were deleted from exception messages intentionally.

RdXmlFile started showing in various youtubes/blogs and it's very much undesirable. It was never meant for public consumption. The format is really bad and the problem it's trying to fix is even worse.