[bugfix] Fixes #16852 by adding click_x and click_y variables to resolve actions

[pblottiere]

Description

Layer actions triggered by identify + right click don't have click_x and click_y variables populated (see https://issues.qgis.org/issues/16852).

Some tests have been added.

This PR supersedes #5071.

Checklist

• Commit messages are descriptive and explain the rationale for changes
• Commits which fix bugs include fixes #11111 in the commit message next to the description
• Commits which add new features are tagged with [FEATURE] in the commit message
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• I have read the QGIS Coding Standards and this PR complies with them
• This PR passes all existing unit tests (test results will be reported by travis-ci after opening this PR)
• New unit tests have been added for core changes
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[pblottiere]

@m-kuhn I think you had reviewed the initial work. Can you give me your opinion on this PR if you have some time?

Thank you!

[pblottiere]

I'll merge this PR tomorrow if no comments come in the meantime.

[m-kuhn]

I don't have the implementation in mind completely right now, please bear with me ;)

Is there a QgsAction for each menuitem (or other means to trigger it) or a (shared) one in the registry? I.e. is there a risk of concurrency / race condition when an action is displayed in the feature form and the attribute table at the same time and both use this setter for different scopes on the same action?

[pblottiere]

According to the QgsActionMenu::reloadActions method, it seems that there's well a QgsAction for each item in the menu. So I don't think there's a risk of concurrency in this case.

[m-kuhn]

Thanks, good for me then