Analyzer suggestion: Prefer SafeHandle over IntPtr

[Mrnikbobjeff]

After working on some Interop analyzers I thought about SafeHandle and how known api's could suggest using the corresponding safehandle, such as SafeFileHandle or SafeWaitHandle. This could also more broadly be applied based on the method name, e.g. methods contains alloc/free could offer a warning when an IntPtr is used instead of a custom safehandle.

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[jeffschwMSFT]

@elinor-fung can you take a look?

[elinor-fung]

I'd be concerned with false positives with any attempt to use the method name. For known APIs, this seems reasonable, however we have #42550, where marshalling SafeHandle doesn't allow null. We would need to address that issue before adding an analyzer like this.

/cc @AaronRobinsonMSFT @jkoritzinsky

[AaronRobinsonMSFT]

@elinor-fung Let's make sure we fold this into #37039.

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