Make src_paths behave as expected when using --resolve-all-configs and improve performance

[sudowork]

When using --resolve-all-configs, there is unexpected behavior in that src_paths ends up resolving relative to the project root, which defaults to the current working directory. This results in first-party modules being marked as third-party modules in the default case.

Under the previous implementation, one possible workaround would be to specify the relative path to config directory (e.g. relative/path/to/configdir/src). However, assuming that the most common use of --resolve-all-configs is to support multiple sub-projects in the same repository/overall directory, this workaround would now require each sub-project to understand where it lives in the filesystem.

This change proposes a fix that sets directory on the config_data to be the directory containing the used configuration file if not already set. Downstream, this directory is then used to resolve the absolute paths specified by src_paths.

This change also introduces performance improvements to find_all_configs by pruning as we walk the filesystem and other smaller performance enhancements.

Fixes #2045

[sudowork]

One thing of note: This would be backwards incompatible for anyone depending on the behavior of resolving first-party src_paths from the project root or config root. However, my assumption is that the behavior this change introduces is what users would expect given the types of config files we look for (.isort.cfg, pyproject.toml, setup.cfg, tox.ini, .editorconfig). The only odd one out in my opinion would be .editorconfig, which supports having a non-root configuration; however, given the behavior of the --resolve-all-configs flag to only choose the closest config file, I opted to not handle this case for consistency and to avoid further complicating the code.

This change also makes the behavior consistent with configuring a settings path.

[sudowork]

This is the main logic to fix the src_paths resolution.

[sblask]

I just ran into this problem. I have a mono repo with multiple python projects in sub folders that each have an .isort.cfg. When running isort from the root on a file in directory one, everything works as expected, same on a file in directory two. But when I run on a file from directory one and two at the same time (when using pre-commit), only one of the files is formatted correctly. I thought --resolve-all-configs would solve this, but quite the opposite, when using it, neither works. I'd expect the folder with the config file to be set as root for the files in them. Sounds like this PR would solve this?