[patch] More details are needed for "Tag value longer than allowed"

[naoliv]

Have any object with a very long fixme tag, for example and validate it.
JOSM says: Tag value longer than allowed - Key 'fixme' invalid

But the user probably doesn't know the maximum number of allowed characters nor he knows how much chars he need to remove to have a valid value again.

Could JOSM, if possible, display length(value)/255 chars (or something like that) together with the message?

JOSM:

Relative:URL: ^/trunk
Repository:UUID: 0c6e7542-c601-0410-84e7-c038aed88b3b
Last:Changed Date: 2017-10-17 21:49:06 +0200 (Tue, 17 Oct 2017)
Revision:13016
Build-Date:2017-10-18 01:31:45
URL:http://josm.openstreetmap.de/svn/trunk

Identification: JOSM/1.5 (13016 en) Linux Debian GNU/Linux unstable (sid)
Memory Usage: 444 MB / 3072 MB (190 MB allocated, but free)
Java version: 9-Debian+0-9b181-4, Oracle Corporation, OpenJDK 64-Bit Server VM
Screen: :0.0 1920x1080
Maximum Screen Size: 1920x1080
Java package: openjdk-9-jre:amd64-9~b181-4
Java ATK Wrapper package: libatk-wrapper-java:all-0.33.3-13
VM arguments: [--illegal-access=warn, --add-modules=java.se.ee, -Dawt.useSystemAAFontSettings=on]
Program arguments: [--language=en]
Dataset consistency test: No problems found

[mmd]

(side note: 255 are really characters, not bytes - which is important in the context of utf-8 multibyte chars)

[Klumbumbus]

Patch attached. Please review.

[Don-vip]

"255" should be parameterized in case the limit changes or we want to reuse the translated string for something else.

[Don-vip]

In 13414/josm:

fix #15452 - More details are needed for "Tag value longer than allowed" (patch by Klumbumbus, modified)