Missing doc: How should paths starting with /_framework be resolved?

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After a fruitless google search I searched dotnet docs for _framework and found only two hits, both kind of useless. I also tried `C:\Program Files\dotnet>dir _framework /a:d /s` which was also ineffective as nothing matches.

**Describe the new article**

dotnet watch works by injecting scripts with /_framework. This doesn't work properly when using a custom static file provider. (Which we use because of a different bug.) We can easily detect when we are running under debug environment and should resolve /_framework paths but no idea how to provide the files.

I suspect it's serving files out of C:\Program Files\dotnet but I have no idea how to find them.

Document outline probably works as follows:

When using a custom static file provider, `dotnet watch` doesn't work.

_framework should resolve to this (fill in) directory within dotnet shared runtime whenever the environment variable `__ASPNETCORE_BROWSER_TOOLS` is set.

To locate this directory on Windows, ...

To locate this directory on Mac OSX, ...

To locate this directory on Linux ...

Seems pretty short.

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#### Document Details

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* ID: 16f49f1b-261c-8cd0-a024-32c2535d0a0f
* Version Independent ID: 218d2a4d-2ff3-8e4d-1f06-bbb3710878fe
* Content: [dotnet watch command - .NET CLI](https://learn.microsoft.com/en-us/dotnet/core/tools/dotnet-watch)
* Content Source: [docs/core/tools/dotnet-watch.md](https://github.com/dotnet/docs/blob/main/docs/core/tools/dotnet-watch.md)
* Product: **dotnet-fundamentals**
* Technology: **dotnet-cli**
* GitHub Login: @tdykstra
* Microsoft Alias: **tdykstra**