Generalize workaround for taskw character encoding

The Logseq and Todoist plugins both implement a workaround for characters `"` `[` and `]` getting URL encoded as `&dquote;` `&open;` and `&close;` in the taskwarrior task description and content by replacing the over-encoded characters with alternate `'` `〈` and `〉` to avoid the encoding logic.

This issue is originally discussed [here](https://github.com/GothenburgBitFactory/bugwarrior/pull/1052#discussion_r1649885645) in the Logseq PR, and again [here](https://github.com/GothenburgBitFactory/bugwarrior/pull/1101#discussion_r2214269600) in the Todoist PR.

The root cause of the issue in the `taskw` python package https://github.com/ralphbean/taskw/issues/172

While this issue remains unresolved in `taskw`, or until replacement package is used https://github.com/GothenburgBitFactory/bugwarrior/issues/1078, it's proposed to move the character replacement method to the base `Issue` class and apply it to the relevant fields in every service.