## Summary of the Pull Request
This adds support for the [`DECSCNM`](https://vt100.net/docs/vt510-rm/DECSCNM.html) private mode escape sequence, which toggles the display between normal and reverse screen modes. When reversed, the background and foreground colors are switched. Tested manually, with [Vttest](https://invisible-island.net/vttest/), and with some new unit tests.
## References
This also fixes issue #72 for the most part, although if you toggle the mode too fast, there is no discernible flash.
## PR Checklist
* [x] Closes#3773
* [x] CLA signed. If not, go over [here](https://cla.opensource.microsoft.com/microsoft/Terminal) and sign the CLA
* [x] Tests added/passed
* [ ] Requires documentation to be updated
* [ ] I've discussed this with core contributors already. If not checked, I'm ready to accept this work might be rejected in favor of a different grand plan. Issue number where discussion took place: #xxx
## Detailed Description of the Pull Request / Additional comments
I've implemented this as a new flag in the `Settings` class, along with updates to the `LookupForegroundColor` and `LookupBackgroundColor` methods, to switch the returned foreground and background colors when that flag is set.
It also required a new private API in the `ConGetSet` interface to toggle the setting. And that API is then called from the `AdaptDispatch` class when the screen mode escape sequence is received.
The last thing needed was to add a step to the `HardReset` method, to reset the mode back to normal, which is one of the `RIS` requirements.
Note that this does currently work in the Windows Terminal, but once #2661 is implemented that may no longer be the case. It might become necessary to let the mode change sequences pass through conpty, and handle the color reversing on the client side.
## Validation Steps Performed
I've added a state machine test to make sure the escape sequence is dispatched correctly, and a screen buffer test to confirm that the mode change does alter the interpretation of colors as expected.
I've also confirmed that the various "light background" tests in Vttest now display correctly, and that the `tput flash` command (in a bash shell) does actually cause the screen to flash.
We now truncate the font name as it goes out to GDI APIs, in console API
servicing, and in the propsheet.
I attempted to defer truncating the font to as far up the stack as
possible, so as to make FontInfo usable for the broadest set of cases.
There were a couple questions that came up: I know that `Settings` gets
memset (memsat?) by the registry deserializer, and perhaps that's
another place for us to tackle. Right now, this pull request enables
fonts whose names are >= 32 characters _in Windows Terminal only_, but
the underpinnings are there for conhost as well. We'd need to explicitly
break at the API, or perhaps return a failure or log something to
telemetry.
* Should we log truncation at the API boundary to telemetry?
-> Later; followup filed (#3123)
* Should we fix Settings here, or later?
-> Later; followup filed (#3123)
* `TrueTypeFontList` is built out of things in winconp, the private
console header. Concern about interop structures.
-> Not used for interop, followup filed to clean it up (#3123)
* Is `unsigned int` right for codepage? For width?
-> Yes: codepage became UINT (from WORD) when we moved from Win16 to
Win32
This commit also includes a workaround for #3170. Growing
CONSOLE_INFORMATION made us lose the struct layout lottery during
release builds, and this was an expedient fix.
Closes#602.
Related to #3123.
