## Summary of the Pull Request

This improves our `RIS` (hard reset) implementation, so it now also
resets any changes that are made to the color table and color aliases,
which is one of the things it's supposed to be doing.

## References and Relevant Issues

This is also a small step towards implementing the `OSC` sequences that
reset individual color table entries (issue #3719).

## Detailed Description of the Pull Request / Additional comments

The way this works is by having a second copy of the color table and
alias indices to hold the default values in the `RenderSettings` class.
This default set is initially populated at startup with the user's
chosen color scheme, but can also potentially be updated if the user
changes their settings while a session is already in progress.

When we receive an `RIS` request, we just copy the default values back
over the active settings, and refresh the renderer.

## Validation Steps Performed

I've manually tested both OpenConsole and Windows Terminal by changing
my color scheme programmatically, and then confirming that the original
colors are restored when an `RIS` sequence is received.

I've also added some basic unit tests that check both the color aliases
and color table are restored by `RIS`.

## PR Checklist
- [x] Tests added/passed

(cherry picked from commit 5e8e10f)
Service-Card-Id: PVTI_lADOAF3p4s4AmhmQzgTTOyY
Service-Version: 1.22

This pull request adds support for resetting the various color table
entries and xterm resource values back to their defaults.

Building on the default color table James introduced in #17879, it was
relatively straightforward to add support for resetting specific
entries.

This implementation cleaves tightly to observed behavior in xterm(379)
rather than observed behavior in libvte(0.70.6). They differ in the
following ways:

- xterm rejects any OSC [110..119] with any number of parameters; libvte
accepts it but only resets the first color.
- When passed a list of color indices to reset in 104, xterm resets any
colors up until the first one which fails to parse as an integer and
does _not_ reset the rest; libvte resets all parseable color indices.

I was unable to verify how these reset commands interact with colors set
via `DECAC Assign Color` so I went with the implementation that made the
most sense:

- Resetting the background color with `110` also restores the background
color alias entry to its pre-`DECAC` value; this results in the
perceived background color returning to e.g. index 0 in conhost and the
`background` color in Terminal.
- _ibid._ for the foreground color

Refs #18695
Refs #17879
Closes #3719

This pull request adds support for resetting the various color table
entries and xterm resource values back to their defaults.

Building on the default color table James introduced in #17879, it was
relatively straightforward to add support for resetting specific
entries.

This implementation cleaves tightly to observed behavior in xterm(379)
rather than observed behavior in libvte(0.70.6). They differ in the
following ways:

- xterm rejects any OSC [110..119] with any number of parameters; libvte
accepts it but only resets the first color.
- When passed a list of color indices to reset in 104, xterm resets any
colors up until the first one which fails to parse as an integer and
does _not_ reset the rest; libvte resets all parseable color indices.

I was unable to verify how these reset commands interact with colors set
via `DECAC Assign Color` so I went with the implementation that made the
most sense:

- Resetting the background color with `110` also restores the background
color alias entry to its pre-`DECAC` value; this results in the
perceived background color returning to e.g. index 0 in conhost and the
`background` color in Terminal.
- _ibid._ for the foreground color

Refs #18695
Refs #17879
Closes #3719

(cherry picked from commit 5f31150)
Service-Card-Id: PVTI_lADOAF3p4s4AmhmQzgZOWsU
Service-Version: 1.22

This pull request adds support for resetting the various color table
entries and xterm resource values back to their defaults.

Building on the default color table James introduced in #17879, it was
relatively straightforward to add support for resetting specific
entries.

This implementation cleaves tightly to observed behavior in xterm(379)
rather than observed behavior in libvte(0.70.6). They differ in the
following ways:

- xterm rejects any OSC [110..119] with any number of parameters; libvte
accepts it but only resets the first color.
- When passed a list of color indices to reset in 104, xterm resets any
colors up until the first one which fails to parse as an integer and
does _not_ reset the rest; libvte resets all parseable color indices.

I was unable to verify how these reset commands interact with colors set
via `DECAC Assign Color` so I went with the implementation that made the
most sense:

- Resetting the background color with `110` also restores the background
color alias entry to its pre-`DECAC` value; this results in the
perceived background color returning to e.g. index 0 in conhost and the
`background` color in Terminal.
- _ibid._ for the foreground color

Refs #18695
Refs #17879
Closes #3719

(cherry picked from commit 5f31150)
Service-Card-Id: PVTI_lADOAF3p4s4AxadtzgZOWsQ
Service-Version: 1.23