This is both a bugfix and a generalization of #25168. In #25168, we attempted to filter padding
*just* from the debug output of `spack.util.executable.Executable` objects. It turns out we got it
wrong -- filtering the command line string instead of the arg list resulted in output like this:
```
==> [2021-08-05-21:34:19.918576] ["'", '/', 'b', 'i', 'n', '/', 't', 'a', 'r', "'", ' ', "'", '-', 'o', 'x', 'f', "'", ' ', "'", '/', 't', 'm', 'p', '/', 'r', 'o', 'o', 't', '/', 's', 'p', 'a', 'c', 'k', '-', 's', 't', 'a', 'g', 'e', '/', 's', 'p', 'a', 'c', 'k', '-', 's', 't', 'a', 'g', 'e', '-', 'p', 'a', 't', 'c', 'h', 'e', 'l', 'f', '-', '0', '.', '1', '3', '-', 'w', 'p', 'h', 'p', 't', 'l', 'h', 'w', 'u', 's', 'e', 'i', 'a', '4', 'k', 'p', 'g', 'y', 'd', 'q', 'l', 'l', 'i', '2', '4', 'q', 'b', '5', '5', 'q', 'u', '4', '/', 'p', 'a', 't', 'c', 'h', 'e', 'l', 'f', '-', '0', '.', '1', '3', '.', 't', 'a', 'r', '.', 'b', 'z', '2', "'"]
```
Additionally, plenty of builds output padded paths in other plcaes -- e.g., not just command
arguments, but in other `tty` messages via `llnl.util.filesystem` and other places. `Executable`
isn't really the right place for this.
This PR reverts the changes to `Executable` and moves the filtering into `llnl.util.tty`. There is
now a context manager there that you can use to install a filter for all output.
`spack.installer.build_process()` now uses this context manager to make `tty` do path filtering
when padding is enabled.
- [x] revert filtering in `Executable`
- [x] add ability for `tty` to filter output
- [x] install output filter in `build_process()`
- [x] tests
7ddd6ad461