Disable Straighten operation when the selection isn't mostly visible

[quincylvania]

For safety, most operations in iD are disabled for features that extend far past the current viewport. I recently added this check for copy/paste (#7603). The Straighten operation is the last obvious outlier, with iD happily straightening entire rivers off-screen as long as the nodes are all on downloaded tiles. We should reduce errors and vandalism by enabling the visibility check when straightening.

Mentioned before in #2248 (comment) and #5236.