Top legend not taken into account for vislib chart height

[flash1293]

Kibana version: master

Elasticsearch version:

Server OS version:

Browser version:

Browser OS version:

Original install method (e.g. download page, yum, from source, etc.):

Describe the bug: If a top legend is chosen for vislib chart types, the chart overflows the x axis on the bottom of the chart.

Steps to reproduce:

1. Create area chart with non-empty top legend and x axis on the bottom
2. Add to dashboard

Expected behavior:
The additional height of the legend should be taken into account for the chart height.

Screenshots (if relevant):

Errors in browser console (if relevant):

Provide logs and/or server output (if relevant):

Any additional context:

[elasticmachine]

Pinging @elastic/kibana-app (Team:KibanaApp)

[flash1293]

cc @nickofthyme could you check out whether that happened during the migration of legend/vislib?

I fixed a similar bug in 7.0, might be related: #30960

[nickofthyme]

@flash1293 I'll take a look. I think I know what the issue might be.