Speed up ANSI code processing (#2368)

This commit speeds up the parsing/processing of ANSI escape codes by
roughly 7.5x. The speedup is mostly accomplished by replacing the regex
with dedicated parsing logic (nextAnsiEscapeSequence()) and reducing the
number of allocations in extractColor().

#### Benchmarks
```
name             old time/op    new time/op     delta
ExtractColor-16    4.89µs ± 5%     0.64µs ± 2%   -86.87%  (p=0.000 n=9+9)

name             old speed      new speed       delta
ExtractColor-16  25.6MB/s ± 5%  194.6MB/s ± 2%  +661.43%  (p=0.000 n=9+9)

name             old alloc/op   new alloc/op    delta
ExtractColor-16    1.37kB ± 0%     0.31kB ± 0%   -77.31%  (p=0.000 n=10+10)

name             old allocs/op  new allocs/op   delta
ExtractColor-16      48.0 ± 0%        4.0 ± 0%   -91.67%  (p=0.000 n=10+10)
```