Check usage of `Series[bool]` and see if `MaskType` is more appropriate

[Dr-Irv]

In #862 a change was made to replace Series[bool] with MaskType for .loc. There are other places in the stubs where Series[bool] is used, and we should investigate which of those usages as arguments (not as return types) should be replaced with MaskType

[ramvikrams]

I'll take this up.