Add array type hints to minor methods in the Html class

Add array type hints to minor methods in the Html class

I'm aware that adding these type hints does have the potential of beeing
a breaking change if a caller misuses it. Note that it really is a misuse
in this case because all these parameters are documented as "array" and
nothing else.

I double-checked the usages of all methods I touched and could not find
any caller that does not fulfill the contract of these methods - in other
words, all callers I can find in my local code base (which includes all
major extensions like Echo, Flow, Parsoid, VisualEditor and so on) pass
arrays to these parameters.

I left the main methods openElement, rawElement and so on untouched
because they are called way to often (500 times and more).

Change-Id: I5ca13b26fb08d732ce4cadc4ee3d38314e606fd3