Create a host symbol for host RID (or RID components) for use in templates

[baronfel]

Is your feature request related to a problem? Please describe.

Today we provide the following Host-provided symbols for binding:

• HostIdentifier
• WorkingDirectory

We should make it easier for template authors to create per-architecture defaults/options by providing the current host RID as another symbol/bindable value.

Describe the solution you'd like.

We should provide two new symbols to allow template authors to condition code/assets/symbols/etc based on host OS and host architecture.

• HostPlatform // e.g. win, macos, linux - the first part of the RID. May be dynamic because it is powered by the RID graph.
• HostArchitecture // eg. x64, arm64, x85 - the second logical part of the RID. May be dynamic because it is powered by the RID graph.

Additional context

No response

[marcpopMSFT]

I assume you are proposing Host* for these to be consistent with the existing Identifier one?

[baronfel]

Yeah, exactly - then if we needed an override or to change/let the user specify a different one there might be a Target* variant of those same properties.

[jsturtevant]

I would find this useful as well. I tried using the OS as described in #7405 but found that it only works on Windows. In my use case I need to know if I am on Linux or MacOs as well.