Rollup merge of #39983 - AndrewGaspar:rust-windbg, r=brson

Adds rust-windbg.cmd script

Adds rust-gdb/rust-lldb equivalent for windbg that loads the Rust .natvis files on start.

This change modifies the bootstrap code to add rust-windbg to bin and the .natvis files to lib/rustlib/etc.

Example usage from cmd or PowerShell:
```
rust-windbg -c "bu rs_f442289d74765418!rs::main;g" target\debug\rs.exe
```