Consistent trailing newlines

[silverwind]

To avoid discussions and diffs like https://github.com/nodejs/node/pull/9379/files#r85787597, we could enable EditorConfig's option to enforce a final newline:

insert_final_newline = true

For js files, this could additionally be enforced through the eol-last linter rule. If we decide to do it, we need to assert which files we want to include in .editorconfig. I think anything except deps and likely test assets should be good.

cc: @thefourtheye @addaleax @cjihrig @princejwesley @lpinca

[cjihrig]

SGTM. I think we'd want to include test/ too, but it would probably come down to how many files needed to change.

[silverwind]

Yes, test and test assets should be included. If necessary we can change tests.

[silverwind]

Suprisingly, we're already pretty consistent (or I'm doing something wrong):

$ find . -type f -not -path "./deps/*" -not -path "./out/*" -not -path "./tools/eslint/*" -not -path "./tools/gyp/*" -not -path "./tools/icu/*" -not -path "./tools/msvs/*" -not -path "*/node_modules/*" -iregex '.*\.\(js\|cc\|h\|d\|man\|manifest|\rc\|md\|mardown\|eslintrc\|py\|txt\|sh\|pl\|json\|pem\|key\|crt\|ini\|cnf\|html\|css\)$' | xargs sed -i -e '$a\'
$ git diff --name-only
benchmark/README.md
doc/api_assets/sh_javascript.min.js
test/fixtures/elipses.txt
test/fixtures/fixture.ini
test/fixtures/invalid.json
test/fixtures/keys/agent1-pfx.pem
test/fixtures/msca.pem
test/fixtures/test-error-first-line-offset.js
test/fixtures/url-tests.json
test/fixtures/x1024.txt

[silverwind]

Filed #9410.