added warning when changeset comment length > 255 chars

[alanb43]

Added a simple fix for the issue described in #9374 and #7943. I simply insert a warning message / box in the same format that the existing Google warning appears when the user exceeds 255 characters in their changeset message.

#6817 describes some edge cases that seem to work fine with this change, shown below:

"ZALGO" contains 58 javascript characters (source), here we see exactly 255 characters being calculated as 'good' using 4 * 58 of the demon string + 18 normal chars.

If we add one, we see the new warning:

I also have come to understand that there is a more in-depth fix being worked on in #9390, but this was made as a much simpler fix that follows suit of an existing warning.

[tyrasd]

Thanks for this, @alanb43.

The main difference to #9390 is that this PR only addresses the issue for the changeset comment field. The problem of too long strings is however also present on input fields for any OSM tag (see bug #6817). It's not as often encountered for regular tags, but there are also some somewhat common cases (e.g. a long note, description or source tag).

I think that your PR has the benefit that it stylistically matches the existing warnings for other changeset comment mistakes. I think it would be best for the changeset comment if we combine the length indicator widget from #9390 with the warning message from this PR. What do you think?

[alanb43]

I agree with this and have been tinkering for a bit now trying to do it, without much luck. Will let you know if I make progress here though!

[tyrasd]

This is now integrated into #9390. Thanks again!