* Replace use of `testChdir` with `t.Chdir`
* Update tests to use temporary directories with copied content, instead of using directories in the repo directly.
* Remove stacks copy of testChdir function
This has been replaced with t.Chdir from the standard library
* Replace remaining simple usage of testChdir
* Update guidance for using `tempWorkingDir`
* Replace use of testChdir in a function reused in a single test
* Update comments to no longer recommend using testChdir
* Remove testChdir function!
This is part of a general effort to move all of Terraform's non-library
package surface under internal in order to reinforce that these are for
internal use within Terraform only.
If you were previously importing packages under this prefix into an
external codebase, you could pin to an earlier release tag as an interim
solution until you've make a plan to achieve the same functionality some
other way.
