Standardize file encoding and newlines across repository

[rjmholt]

PR Summary

Alternate approach to #1567.

This PR:

• Adds an .editorconfig file to declare all the various settings for text files in the repo
• Puts all test assets under a common path, so we can ensure that things like encodings and trailing whitespace that might be needed for test cases aren't touched
• Converts all text files that aren't test assets to have the correct encoding and line endings

PR Checklist

• PR has a meaningful title
  • Use the present tense and imperative mood when describing your changes
• Summarized changes
• Change is not breaking
• Make sure all .cs, .ps1 and .psm1 files have the correct copyright header
• Make sure you've added a new test if existing tests do not effectively test the code changed and/or updated documentation
• This PR is ready to merge and is not Work in Progress.
  • If the PR is work in progress, please add the prefix WIP: to the beginning of the title and remove the prefix when the PR is ready.

[xtqqczze]

@rjmholt Please could you resolve merge conflicts.