Deprecate `room=class`; use `room=classroom` instead

[winstonsung]

Bug: #1355 Change-Id: I90545a86f84877fea5908fd097334b87b98682e7

Description, Motivation & Context

"classroom" is now a conpound word and being used more frequently than the old 2-word "class room" in English language.

~~The page "Tag:room=classroom" was created first.~~

~~The page "Tag:room=class" was never created as a non-redirect page.~~

Note also that documentation of tagging on the OpenStreetMap Wiki is not the final arbiter of 'correct' tagging.

Links and data

Relevant OSM Wiki links:

• https://wiki.openstreetmap.org/wiki/Tag:room%3Dclassroom

Relevant tag usage stats:

• https://taginfo.openstreetmap.org/tags/room=class
• https://taginfo.openstreetmap.org/tags/room=classroom
• https://taghistory.raifer.tech/#***/room%3Dclass/&***/room/classroom

Checklist and Test-Documentation Template

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## Test-Documentation

### Preview links & Sidebar Screenshots

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### Wording

- [ ] American English
- [ ] `name`, `aliases` (if present) use Title Case
- [ ] `terms` (if present) use lower case, sorted A-Z
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