Reorganize components/ and lib/

[alexcjohnson]

Sparked by a comment by @etpinard #3254 (comment):

It might be nice to make a distinction between "registerable" (i.e optional) component modules (e.g. annotations/, shapes/) and component modules that are mostly intended to DRY things up (e.g. color/, colorscale/ ... and the soon-to-be axes/). Maybe the latter could be placed in different directory e.g. src/common/ and leave src/components/ for "registerable" modules?

Completely agree we should be clearer about what components/ means. My gut reaction is actually to go even further: common/ serves the same role as lib/, and lib/ itself has perhaps outgrown its origin as a flat directory that exports everything in one namespace. In fact it already doesn't do this, these files are in lib/ but not incorporated in lib/index:
clear_gl_canvases, events, geo_location_utils, geojson_utils, gl_format_color, gup, override_cursor, polygon, prepare_regl, queue, show_no_webgl_msg, str2rgbarray, svg_text_utils, topojson_utils

So my proposal:

• lib/index should only contain small functions that have no dependencies on anything else in our codebase (except constants/; currently it also imports d3 and fast-isnumeric, those seem fine), so it can be safely imported by anyone including other files inside lib/, and it should not import anything else from lib/. This would require most consumers of lib/ to pull in the individual pieces they need rather than just require('../../lib') - that's probably the most controversial part of this proposal, as it would be a bunch of work, but I think it would be an improvement in terms of being explicit about imports, and it would let us 🔪 dumb files like lib/mod and lib/noop that exist only so other lib consumers can import them. It could also reduce the size of partial bundles a little bit.
• We move unregisterable "components" to be subdirectories of lib/
• We try to group other files in lib into subdirectories too - in fact some of the above-mentioned lib files could go into components/color -> lib/color - but I also don't see anything wrong with leaving some hard-to-categorize files directly in lib/.

[gvwilson]

Hi - this issue has been sitting for a while, so as part of our effort to tidy up our public repositories I'm going to close it. If it's still a concern, we'd be grateful if you could open a new issue (with a short reproducible example if appropriate) so that we can add it to our stack. Cheers - @gvwilson