Allow seeing the whole Custom Background URL one is entering

[jidanni]

Allow seeing the whole Custom Background URL one is entering, like JOSM.
JOSM has an entire huge box, but iD has just this tiny textbox which is never enough.

One needs to see the whole thing one entered, so one can be totally sure. Even if one can poke around the various parts.
Never mind my blue highlighting in the image.

[bhousel]

What does it look like in JOSM?

[jidanni]

https://josm.openstreetmap.de/wiki/Help/Preferences/Imagery

[bhousel]

If we change this, we'd need to replace this window.prompt call with a new modal dialog box that can show a textfield. (window.prompt can only do one line, and we don't have any options to customize it)

iD/modules/ui/background.js

Lines 106 to 109 in 73f78c3

	var template = window.prompt(
	t('background.custom_prompt', { example: example }),
	_customSource.template() || example
	);

[manfredbrandl]

I would like iD to remember the custom URL templates for me.

[bhousel]

tagging @vershwal - this is kind of the same as #4806

[bhousel]

More context - this issue will be closed if we replace the window.alert box with a modal screen. We'll be able to replace the single line input with an actual textarea that shows multiple lines.

[bhousel]

This was done in #5207