fix #12114 DynamicLegend broken layout

[stefanocudini]

Description

Fix issue #12114

• fix DynamicPanel layout size on map update layout
• improve exists tests

What kind of change does this PR introduce? (check one with "x", remove the others)

• Bugfix

Issue

What is the current behavior?

dynamicLenged panel layout is broken when window is resized

What is the new behavior?
Test enagle DynamicLegend and resize window, look video below:

legend.mp4

Breaking change

Does this PR introduce a breaking change? (check one with "x", remove the other)

• Yes, and I documented them in migration notes
• No

Other useful information

To replicate enable DynamicLegend adding con desktop in localConfig.json:

   {
      "name": "DynamicLegend",
      "glyph": "align-left",
      "title": "plugins.DynamicLegend.title",
      "description": "plugins.DynamicLegend.description",
      "dependencies": ["SidebarMenu"]
    }