Chore: Reorganizing tests to align with project structure

[platinumazure]

Similar to ESLint and other projects in the ESLint organization, I reorganized the tests so that for each source file path/to/src.js, there would be a test file tests/path/to/src.js. (I renamed "test" to "tests" as part of that effort)

In order to make that work, I needed to change two things related to the mocha invocation:

1. Pass a glob pattern `"tests/*/.js" to pick up all JS files in the tests directory.
2. Move the temp directory out of tests, since unfortunately, some files are left between tests, including generated .js files which shouldn't be run as tests.

If this is acceptable, great; otherwise, let me know how I should improve this. Some possibilities:

• Use a more specific glob pattern (e.g., "tests/{app,lib,plugin,rule}/*.js") to avoid picking up temp
  • Risk: If new test folders are added, package.json must be updated each time
• Ensure tests clean up the test directory after themselves (even if exceptions are thrown)

[nzakas]

LGTM