fix(ui5-split-button): restrict height manipulation from outside wrapper

[hinzzx]

Previously when our ui5-split-button component was wrapped in a container with defined height, f.e:

<div style="border: 1px solid red; height: 80px">
	<ui5-split-button style="width: 100%;" icon="picture">Random Text</ui5-split-button>
</div>

The button was filling the whole space in the container, which wasn't the desired behaviour:

Now the ui5-split-button's height is not based on outside wrappers.

Fixes: #8705

[unazko]

Works as stated.