Remove EdgeHTML support

[rachel-fenichel]

Is your feature request related to a problem? Please describe.

The Edge browser used to use the EdgeHTML browser engine, but has not done so since version 79. Our checks for Edge in useragent.js were actually looking for EdgeHTML. It is now fully deprecated, so we can remove these workarounds.

Describe the solution you'd like

• Remove uses of userAgent.EDGE in Blockly core.
• Remove isEdge and EDGE from useragent.ts
• Remove EdgeHTML workarounds from stripped-down base.js Left in to match upstream base.js

Describe alternatives you've considered

Leave them in. Rejected as extra ongoing maintenance for something that is not used.

Additional context

Inspecting user agent strings is strongly discouraged because they often contain misleading information--for instance, the Edge browser uses the Blink browser engine.

Found while looking into user agent strings for #6336.

[cpcallen]

Remove EdgeHTML workarounds from stripped-down base.js

From a maintenance point of view it is better that the implementations in base-minimal.js be identical to the ones in the upstream Closure-supplied base.js. So until Closure drops support we should not either.