#935 Adjusted computation of horizontal toolbar size to account for inner control

[mh2207yatta]

Fixes #935

[github-actions]

Test Results

     299 files  ±0       299 suites  ±0   5m 39s ⏱️ -3s
  4 096 tests ±0    4 088 ✔️ ±0    8 💤 ±0  0 ❌ ±0 
12 200 runs  ±0  12 127 ✔️ ±0  73 💤 ±0  0 ❌ ±0 

Results for commit 904574c. ± Comparison against base commit 27feab2.

[HeikoKlare]

I addition to my validation of this PR that I have posted in the according issue #935, I have one further finding:

Each view can have its own toolbar. This toolbar is placed (right aligned) in the same row as the view tab headers in case there is sufficient space. Otherwise, the toolbar is placed below the tab headers.
However, with this change, the toolbar will always be placed below the tab header.

This is how it looked before:

And this is how it looks now:

[iloveeclipse]

See last comment, rendering is broken.