checker, orm: add error for unchecked option multi return types, fix undefined behavior

[ttytm]

Fixes #17874
Fixes #21117
Due to the changes, a fix to the vlib orm module is included.

fn split(str string) ?(string, string) {
	return none
}

fn main() {
	foo, bar := split('foo/bar')
	println('${foo}.${bar}')
}

Will now throw:

error: split() returns `?(string, string)`, so it should have either an `or {}` block, or `?` at the end
    4 | 
    5 | fn main() {
    6 |     foo, bar := split('foo/bar')
      |                 ~~~~~~~~~~~~~~~~
    7 |     println('${foo}.${bar}')
    8 | }

Based on #21105 (After resolving it first, the PR should rebased)

Superseeds #20515. The PR is stale for a while, but took good steps towards the solution.

[JalonSolov]

Not a good to idea mention tuples at all. V doesn't support tuples, only multi-returns.

[ttytm]

Ok thanks @JalonSolov gonna update.
Wasn't sure as we have ast.Tuple and ast.TupleType and also the changelog mentions

• Fix returning an option tuple - fn f() ?(int,int) { return g() } (cgen: fix return option call (fix #18848) #18851)

[spytheman]

Excellent work 🚀 .