Drop support for IE11

[mbrzakovic]

Motivation

• Continuing to support IE adds on maintanence burden.
• Dropping the support would simplify and unblock switch to es-build.
• Support for IE is generally decreasing with EOL date for certain OS is set for mid 2022.

Current status

• iD editor works in IE11, however the user editting experience is bad - inconsistent ui elements, unexpected pointer events etc.
• osmwebsite stats show that iD editor is getting <10 hits daily via IE11, ~0.1% of all hits
• Few members have voted in favor of dropping the support and RapiD is planning on doing the same (Drop support for IE11 facebook/Rapid#387). This and some additional info is available in Devbuild on esbuild #8774

Tasks

• If I am reading Is IE11 still supported? #8527 correctly, it seems that the current phantomJS has a dependency on legacy build, however switching to karma Switch to karma #8764 should unblock this.
• I don't have a full context on the development of the IE11 specific features in the past, however here are todo items that I am aware of (cc @bhousel to double-check, add missing):

• Merge Switch to karma #8764 (pre-requisite)
• Remove legacy build (package.json commands, config rollup, babel?)
• Polish rest of commands (remove legacy from commands: all, test, switch minify to take iD.js)
• Remove polyfills and IE11 specific code
• Update util/detect.js
• Update information on README, ACCESSIBILITY.md, core.yaml (browser_notice), package.json - browser list
• Double check if osmwebsite can consume iD.js and prior to release update vendor config (notice that currently osm website is serving iD.legacy.js)

[tyrasd]

Let's do this! (see also #8774 (comment))

[tordans]

This is another place that needs to be updated IMO:

iD/CONTRIBUTING.md

Line 327 in fe4f5c9

In order to continue to support older browsers like IE11 and our PhantomJS-based test runner, we also include the [browser-polyfills](https://github.com/tiagomapmarques/browser-polyfills#what-does-it-have) package.

[tyrasd]

632e241 should mostly finalize the drop of IE11 support. Only thing to do and investigate is to adapt the deployment/integration on the openstreetmap-website repo and check if everything works as expected. Also, the "unsupported browser" error message could probably be improved a bit…

[mbrzakovic]

Great work! Yea, that should mostly cover it.

The only thing that I could add is that I think that babel.config.json file in root can be dropped given that it was introduced for legacy build

Also and perhaps minor, the terminology 'modern' can be dropped and some commands/config files renamed. e.g.
build:modern": "node config/esbuild.config.modern.mjs
to
build:js": "node config/esbuild.config.mjs
etc.