Distinguish source fields between changesets and presets

[1ec5]

Copied id-tagging-schema’s Sources field into a separate Source field for use in presets, leaving the Sources field largely unmodified. Also simplified the code to generate indexed variants of the Source field. This effectively restores the original combo box Sources field to the changeset editor, where we haven’t implemented multiple source fields and don’t expect as much source metadata as on elements. iD does some magic with the changeset-only Sources field that we don’t want to get in the way of.

Fields that can appear multiple times now use stringsCrossReference to inherit the label from the original base field with the index appended, all independently of the raw key. Added parentheses around the index in the label and localize it according to the current locale’s numeral system.

Fixes OpenHistoricalMap/issues#1275.

[1ec5]

To verify that this fixes OpenHistoricalMap/issues#1275, I pointed my local copy to an OAuth application I registered on api06.dev.openstreetmap.org, saved a changeset with custom source=* values, then tried opening and closing the changeset editor. I also reproduced the issue on staging, set a breakpoint before the error, and manually defined sourceField.impl.setCustomOptions() as a no-op to verify that this prevents the error.

[1ec5]

For convenience when reviewing this pull request, it does not include changes that result from running npm run build or npm run dist. We’ll have to rebuild iD before deploying it to staging. OpenHistoricalMap/issues#1342 tracks making this a normal part of the branch management process.

[erictheise]

Not possible to test without incorporating into ohm-website.