Tweak .editorconfig and line endings

- Use `lf` line endings everywhere. This works fine even on Windows, and is more common for git repos. It also matches prettier's default.

For .editorconfig:

- Remove `insert_final_newline = false`: Omitting the final newline isn't supported by prettier or rustfmt.
- Remove `trim_trailing_whitespace = false`: The formatters will remove trailing whitespace anyways. I can't think of a good reason to want to keep trailing whitespace.
- Remove other redundant options.

.gitattributes

@@ -0,0 +1 @@
+* text=auto eol=lf