I was about to add `SetAnsiMode`/`ResetAnsiMode` for `SM` and `RM` when I
realized that we probably don't need yet another enum of mode types, set and
reset functions, and a mode helper for ANSI standard modes when we already have
one for DEC Private modes.
This commit:
1. Changes the enum `PrivateModeParams` to just be `ModeParams`
2. Differentiates ANSI Standard modes (IRM, KAM, SRM, ...) from DEC
Private modes (DECCOLM, DECCKM, ...) using a flag bit set in the enum
value.
3. Introduces a helper class for constructing these values much like
`VTID`. That helper takes a bitmask and applies it to an input to
produce the final enum value.
4. Dispatches all mode set/reset through a common Set/Reset and
`_ModeHelper` that uses the existing enum values.
[1] These modes are in separate namespaces with some overlap. We want to
differentiate them at dispatch time to ensure that `\e[2h` and `\e[?2h` are
given different treatment, and ensure that `\e[1000h` doesn't activate xterm
mouse mode.
Fixes#8457.
104a4e48bd