EPA: Use custom AnnsIf structure for HsIf and HsCmdIf

Before this the exactprint annotations for HsIf were captured as EpAnn [AddEpAnn]

This meant that for

foo c = if c == '_'; then '.'; else c

the two semicolons and then, else are all just in the [AddEpAnn].

Introduce a custom AnnsIf data structure for the HsIf and HsCmdIf constructors.

Closes #19813 (closed)