## Summary of the Pull Request
Adds support for Italics, Blinking, Invisible, CrossedOut text, THROUGH CONPTY. This does **NOT** add support for those styles to conhost or the terminal.
We will store these "Extended Text Attributes" in a `TextAttribute`. When we go to render a line, we'll see if the state has changed from our previous state, and if so, we'll appropriately toggle that state with VT. Boldness has been moved from a `bool` to a single bit in these flags.
Technically, now that these are stored in the buffer, we only need to make changes to the renderers to be able to support them. That's not being done as a part of this PR however.
## References
See also #2915 and #2916, which are some follow-up tasks from this fix. I thought them too risky for 20H1.
## PR Checklist
* [x] Closes#2554
* [x] I work here
* [x] Tests added/passed
* [n/a] Requires documentation to be updated
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* store text with extended attributes too
* Plumb attributes through all the renderers
* parse extended attrs, though we're not renderering them right
* Render these states correctly
* Add a very extensive test
* Cleanup for PR
* a block of PR feedback
* add 512 test cases
* Fix the build
* Fix @carlos-zamora's suggestions
* @miniksa's PR feedback
* Add support for origin mode (DECOM).
* Added a state machine unit test for the origin mode.
* Prevent the cursor position moving below the bottom margin of the scrolling region if the origin mode is relative.
* Only adjust the relative cursor position for origin mode if the scrolling region is actually set.
* Add some screenbuffer unit tests for the origin mode.
* Enhance the soft reset screenbuffer tests to verify the origin mode is reset.
* Move the origin mode flag constructor assignments into the intializer list.
* Implement XTerm's private mode escape sequence for enabling DECCOLM support.
* Add output engine and screen buffer units test for the private mode 40 escape sequence.
