Filter published files on npm

[TrySound]

For now not gzipped leaflet package is 23mb. There's weird 4mb file .goutputstream-N6HL8X and a lot other stuff which increases node_modules size. files field can fix this with specified whitelist.

[perliedman]

Hi and thanks! This does indeed look like a very good idea.

A question to understand this change: with this change, we include src although not strictly necessary (the main attribute is set to dist/leaflet-src.js). Is this to make it possible to import specific parts of Leaflet as modules, or is the intention to still supply a somewhat complete version of Leaflet? If the later, would it also make sense to include spec?

I'm not too familiar with how npm packages are normally distributed, so trying to understand what would be best for us here.

[TrySound]

Yeah. Source is useful to reduce bundle size, classes are not treeshakable by bundlers. I don't see spec necessary in published package.

[mourner]

This looks good! But given that we already have an .npmignore file, it would be nice to have this in one place — i.e. either in files or npmignore but not both, to make it easier to maintain.

[TrySound]

Sure, forgot to remove :)