feat: allow stack bar only

[JulienMalcouronne]

New Pull Request

When adding multiple lines to an existing stack bar chart, the lines are also stacked rather than being expressed independently. That is, where line series 1 has a value of 10 and line series 2 has a value of 5 series 2 will be plotted at 15, not 5.

New Options:
chart.stackOnlyBar = true
tooltip.hideEmptyShared = true

Fixes #907 & #2076

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

[JulienMalcouronne]

Picture of the expected result with tooltip activated :

[iameddz]

Same as #3477. please merge one of these

[github-actions]

This pull request has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.