## Summary of the Pull Request
When WSL vim prints the initial empty buffer (the one that's just a bunch of '\~'s), it prints this by doing the following:
* Print '\~' followed by enough spaces to clear the line
* Use CUP (`^[[H`) to move the cursor to the start of the next line
* repeat until the buffer is full
When we'd get the line of "\~ "... in conhost, we'd mark that line as wrapped.
Logically, it doesn't really make any sense that when we follow that up by moving the cursor, the line is wrapped. However, this is just how conhost is right now.
This wasn't ever a problem in just conhost before, because we really didn't care if lines in the alt buffer were "wrapped" or not. Plus, when vim would get resized, it would just reprint it's own buffer anyways. Nor was this a problem in conpty before this year (2020). We've only just recently added logic to conpty to try and preserve wrapped lines.
Initially, I tried fixing this by breaking the line manually when the cursor was moved. This seemed to work great, except for the win32 vim.exe. Vim.exe doesn't emit a newline or a CUP to get to the next line. It just _goes for it_ and keeps printing. So there's _no way_ for us to know the line broke, because they're essentially just printing one long line, assuming we'll automatically move the cursor.
So instead, I'm making sure to emit the proper number of spaces at the end of a line when the line is wrapped. We won't do any funny business in that scenario and try to optimize for them, we'll _just print the spaces_.
## References
* #5181 - This change regressed this
* #4415 - Actually implemented wrapped lines in conpty
## PR Checklist
* [x] Closes#5291
* [x] I work here
* [x] Tests added/passed
* [n/a] Requires documentation to be updated
## Validation Steps Performed
* Wrote a unittest first and foremost
* Checked vtpipeterm to make sure vim still works
* checked Terminal to make sure vim still works
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