fix(bash): strip control chars generated by \[\] in PS1 with bash-preexec

[akinomyoga]

Fixes #1617

This contains an extra commit dc2afa7, which counts the newlines in the prompt result using Bash's built-in features. The previous implementations used the external command wc with the command substitution, which involves 3 forks and 1 exec so is slow. We can count newlines by first removing all the characters except for the newlines and then counting the number of remaining characters.

[ellie]

thank you! lots of shell improvements from you, really appreciate it 🙏

[akinomyoga]

Thanks!