Extremely slow performance when processing virtual terminal sequences

### Windows Terminal version (or Windows build number)

1.8.1521.0

### Other Software

_No response_

### Steps to reproduce

Using any command line utility that produces virtual terminal sequences for setting the colors of individual characters, the performance of the terminal drops by a factor of around 40.

To measure this effect precisely, you can use the F2 key in termbench and observe the performance difference between color-per-character output and single-color output:

https://github.com/cmuratori/termbench/releases/tag/V1

### Expected Behavior

Despite the increased parsing load, modern CPUs should not have a problem parsing per-character color escape codes quickly. I would expect the performance of the terminal to be able to sustain roughly the same frame rate with per-character color codes as without, and if there was a performance drop, I wouldn't expect it to be anything close to 40x.

### Actual Behavior

The speed of per-character color output is 40x slower than the speed of single-color output.

Start by reproducing the comparison in termbench using the F2 measurement, contrasting per-character color output with single-color output. Profile the terminal while processing these virtual terminal sequences and identify the source of the roughly 40x slowdown; the work is done when per-character output has substantially improved performance without changing expected rendering.

Written by the indexing model from the issue text.