Windows no std shim

[zsol]

This PR changes the windows shim to drop a lot of dependencies, shrinking the size of the final binary to 4KB.

It's 90% based on @zertosh's work, with a few changes:

• stopped using a Vec and thus the need for a global allocator
• A few extra places for error handling
• Updated the dependencies (windows-sys and compiler_builtins)

[zertosh]

Are you sure this is 4KB? I'll fiddle with Azure and try to get a VM.

Please excuse my bad github skills, I don't know how to do reviews here

[zsol]

Yup, pretty sure it's 4KB. GitHub and PowerShell both say so:

Length Name
------ ----
4096 dotslash_windows_shim-x86_64.exe

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