## Summary of the Pull Request
Introduces `til::rle`, a vector-like container which stores elements of
type T in a run length encoded format. This allows efficient compaction
of repeated elements within the vector.
## References
* #8000 - Supports buffer rewrite work. A re-use of `til::rle` will be
useful as a column counter as we pursue NxM storage and presentation.
* #3075 - The new iterators allow skipping forward by multiple units,
which wasn't possible under `TextBuffer-/OutputCellIterator`.
Additionally it also allows a bulk insertions.
* #8787 and #410 - High probability this should be `pmr`-ified
like `bitmap` for things like `chafa` and `cacafire`
which are changing the run length frequently.
## PR Checklist
* [x] Closes#8741
* [x] I work here.
* [x] Tests added.
* [x] Tests passed.
## Validation Steps Performed
* [x] Ran `cacafire` in `OpenConsole.exe` and it looked beautiful
* [x] Ran new suite of `RunLengthEncodingTests.cpp`
Co-authored-by: Michael Niksa <miniksa@microsoft.com>
