feat(corelib): OptionTrait boolean operators

[julio4]

Boolean operators

These methods treat the [Option] as a boolean value, where [Some] acts like [true] and [None] acts like [false]. There are two categories of these methods: ones that take an [Option] as input, and ones that take a function as input (to be lazily evaluated).

The and, or, and xor methods take another [Option] as input, and produce an [Option] as output. Only the and method can produce an [Option<U>] value having a different inner type U than [Option<T>].

method	self	input	output
and	None	(ignored)	None
and	Some(x)	None	None
and	Some(x)	Some(y)	Some(y)
or	None	None	None
or	None	Some(y)	Some(y)
or	Some(x)	(ignored)	Some(x)
xor	None	None	None
xor	None	Some(y)	Some(y)
xor	Some(x)	None	Some(x)
xor	Some(x)	Some(y)	None

The and_then and or_else methods take a function as input, and
only evaluate the function when they need to produce a new value. Only
the and_then method can produce an [Option<U>] value having a
different inner type U than [Option<T>].

method	self	function input	function result	output
and_then	None	(not provided)	(not evaluated)	None
and_then	Some(x)	x	None	None
and_then	Some(x)	x	Some(y)	Some(y)
or_else	None	(not provided)	None	None
or_else	None	(not provided)	Some(y)	Some(y)
or_else	Some(x)	(not provided)	(not evaluated)	Some(x)

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