Add .editorconfig

.editorconfig is "a file format for defining coding styles" which is
understood by various editors. It can allow for, for example, vscode to
automatically configure whether to use tabs or spaces.

I'm adding it both because my editor seems to incorrectly assume the
Javascript in the project should use spaces, as well as to be a precursor
for adding prettier in a later commit. I've split it off from prettier as
it shouldn't have an effect on the build so should be able to be merged
before CI is able to run on the prettier build.

Signed-off-by: Skyler Grey <skyler.grey@collabora.com>
Change-Id: Id0b1da1388a1fb2706d64623a6d8f35f9a1c605f

.editorconfig

@@ -0,0 +1,9 @@
+root = true
+
+[*]
+end_of_line = lf
+insert_final_newline = true
+
+[*.{js,ts}]
+charset = utf-8
+indent_style = tab