SetConsoleActiveScreenBuffer breaks Unicode output

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### Windows Terminal version

1.22.1972 and newer

### Windows build number

10.0.19045.4412

### Other Software

No

### Steps to reproduce

1. Compile this simple program:
```C++
#include

int main()
{
const auto Output = GetStdHandle(STD_OUTPUT_HANDLE);
DWORD n;
WriteConsole(Output, L"𠜎𠝹𠱓𠱸𠲖𠳏𠳕𠴕𠵼𠵿𠸎\n", 23, &n, {});
WriteConsole(Output, L"💖💫🐶🐇🌎🏃\n", 13, &n, {});
MessageBox({}, L"Press OK", {}, 0);
const auto NewBuffer = CreateConsoleScreenBuffer(GENERIC_READ | GENERIC_WRITE, FILE_SHARE_READ | FILE_SHARE_WRITE, {}, CONSOLE_TEXTMODE_BUFFER, {});
SetConsoleActiveScreenBuffer(NewBuffer);
SetConsoleActiveScreenBuffer(Output);
MessageBox({}, L"See?", {}, 0);
}
```
2. Run it.
3. Follow the instructions.

### Expected Behavior

The text stays intact after pressing OK (and calling `SetConsoleActiveScreenBuffer(Output);`):


### Actual Behavior

The text is broken, as if a bad conversion happens somewhere:


#### Observations

- It stopped working somewhere between WT 1.22.1511.0 (1.22.240530001, 31 May) and 1.22.1972.0 (1.22.240715002, 17 Jul). Unfortunately I don't have any other versions in between.
- OpenConsole is not affected, only WT.

Start by compiling and running the provided C++ reproduction on the affected Windows Terminal versions, comparing behavior with OpenConsole and the listed older version. Trace handling of SetConsoleActiveScreenBuffer and the transition back to the original buffer, then verify that the Unicode output remains intact after the second MessageBox is dismissed.

Written by the indexing model from the issue text.