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(cherry picked from commit 56238d4c)

(cherry picked from commit da77d70f)

(cherry picked from commit b689ef4b)

(cherry picked from commit 12f2da4a)

(cherry picked from commit f9b72d53)

(cherry picked from commit fec624e2)

It has been stuck at 1.3.0 for 28 releases

Test plan:
- removed lib64/plugins/kmplotpart.so
- kmplot still works (finds the part on startup)
- konqueror still allows to preview a fkt file
- lxr shows no other code loading "kmplotpart" by name directly

KF6 task: https://phabricator.kde.org/T12340

* The library name if kmplotpart, not libkmplotpart.
* The -1 was going out of bounds when called with XSection which is 0

Testcase: konqueror <directory_with_a_fkt_file>, right click on .fkt
file, Preview In, KmPlotPart

* Add @title:window helpers and a @action:inmenu
* Suitable capitalization and punctuation

* Update date and version numbers
* Suitable tags, some punctuation and sync with the GUI messages

In case of conflict in i18n, keep the version of the branch "ours"
To resolve a particular conflict, "git checkout --ours path/to/file.desktop"

In case of conflict in i18n, keep the version of the branch "ours"
To resolve a particular conflict, "git checkout --ours path/to/file.desktop"