Use EpicActionsSplitButton in RelatedItemsTreeHeader

Inactive Accountrequested to merge
winh-epics-split-button into master

What does this MR do?

fix #34530 (closed)

Screenshots

Before After
Screen_Shot_2019-10-22_at_16.51.26 Screen_Shot_2019-10-22_at_16.50.20
Screen_Shot_2019-10-22_at_16.51.35 Screen_Shot_2019-10-22_at_16.50.15
Screen_Recording_2019-10-22_at_17.33.21 Screen_Recording_2019-10-22_at_17.34.28
Edited by Inactive Account

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