[ENHANCEMENT] "Set Root Element": Add scope & return current scope

[simonmeggle]

I would like to suggest that the keyword "Set Root Element" to be aligned to the behaviour of the keyword "Set Selector Prefix" in the browser library:
link

Specifically:

• Allow the root element to be limited to a specific RF scope (suite/test/keyword).
• The keyword should return the current root node when called. This makes it easier to perform multiple changes and save the previous root node in a variable.