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 (https://github.com/facebookincubator/RapiD/issues/387). This and some additional info is available in https://github.com/openstreetmap/iD/pull/8774

Tasks

• If I am reading https://github.com/openstreetmap/iD/issues/8527 correctly, it seems that the current phantomJS has a dependency on legacy build, however switching to karma https://github.com/openstreetmap/iD/pull/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):

• [x] Merge https://github.com/openstreetmap/iD/pull/8764 (pre-requisite)
• [x] Remove legacy build (package.json commands, config rollup, babel?)
• [x] Polish rest of commands (remove legacy from commands: all, test, switch minify to take iD.js)
• [x] Remove polyfills and IE11 specific code
• [x] Update util/detect.js
• [x] Update information on README, ACCESSIBILITY.md, ~~core.yaml (browser_notice)~~, package.json - browser list
• [x] 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 https://github.com/openstreetmap/iD/pull/8774#issuecomment-988080734)

[tordans]

This is another place that needs to be updated IMO:

https://github.com/openstreetmap/iD/blob/fe4f5c9548b97b898960b65b3191367fd9864347/CONTRIBUTING.md#L327-L327

[tyrasd]

632e24137a22922718aa1d8c2fd915a154d02879 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.