[Performance] Replace std::vector with more lightweight structure in `RenderData::GetPatternId`

This is about the scrolling test in #10563. A simplified repro would be:

```bash
time bash -c 'yes | head -n1000000'
```

which takes 7-8s with windows terminal and 300ms with gnome terminal.

Test case provided by @lhecker.

These lines show up in the hot paths of the trace of `OpenConsole`:

https://github.com/microsoft/terminal/blob/main/src/renderer/base/renderer.cpp#L788


It appears that simply constructing empty `std::vector` (empty because this is in conhost/OpenConsole) is quite expensive.

CC @PankajBhojwani

Start with RenderData::GetPatternId and the referenced hot path at src/renderer/base/renderer.cpp#L788. Run the provided scrolling repro, `time bash -c 'yes | head -n1000000'`, and inspect the trace showing empty std::vector construction in conhost/OpenConsole. Done means replacing that costly structure appropriately and confirming the scrolling performance improves.

Written by the indexing model from the issue text.