introduce more return type providers

[azjezz]

new return type providers:

• Iter\count return positive-int when $iterable is a non-empty-list<_>.
• Iter\count return positive-int when $iterable is a non-empty-array<_, _>.
• Iter\count return int(0) when $iterable is empty&array<_, _>
• Iter\count return int(x) when $iterable is a non-empty-list<_> with a known count, where x is the size of $iterable.
• Iter\count return int(x) when $iterable is a non-empty-array<_, _> with a known count, where x is the size of $iterable.
• Iter\last return Tv when $iterable is a non-empty-list<Tv>.
• Iter\last return Tv when $iterable is a non-empty-array<_, Tv>.
• Iter\last return null when $iterable is empty&array<_, _>
• Iter\last return Tv when $iterable is array{...} with at least 1 property.
• Iter\first return Tv when $iterable is a non-empty-list<Tv>.
• Iter\first return Tv when $iterable is a non-empty-array<_, Tv>.
• Iter\first return null when $iterable is empty&array<_, _>
• Iter\first return Tv when $iterable is array{...} with at least 1 property.
• Str\after return null|lowercase-string when the first argument is lowercase-string.
• Str\after_last return null|lowercase-string when the first argument is lowercase-string.
• Str\after_ci return null|lowercase-string when the first argument is lowercase-string.
• Str\after_last_ci return null|lowercase-string when the first argument is lowercase-string.
• Str\before return null|lowercase-string when the first argument is lowercase-string.
• Str\before_last return null|lowercase-string when the first argument is lowercase-string.
• Str\before_ci return null|lowercase-string when the first argument is lowercase-string.
• Str\before_last_ci return null|lowercase-string when the first argument is lowercase-string.
• Str\Byte\after return null|lowercase-string when the first argument is lowercase-string.
• Str\Byte\after_last return null|lowercase-string when the first argument is lowercase-string.
• Str\Byte\after_ci return null|lowercase-string when the first argument is lowercase-string.
• Str\Byte\after_last_ci return null|lowercase-string when the first argument is lowercase-string.
• Str\Byte\before return null|lowercase-string when the first argument is lowercase-string.
• Str\Byte\before_last return null|lowercase-string when the first argument is lowercase-string.
• Str\Byte\before_ci return null|lowercase-string when the first argument is lowercase-string.
• Str\Byte\before_last_ci return null|lowercase-string when the first argument is lowercase-string.
• Str\Grapheme\after return null|lowercase-string when the first argument is lowercase-string.
• Str\Grapheme\after_last return null|lowercase-string when the first argument is lowercase-string.
• Str\Grapheme\after_ci return null|lowercase-string when the first argument is lowercase-string.
• Str\Grapheme\after_last_ci return null|lowercase-string when the first argument is lowercase-string.
• Str\Grapheme\before return null|lowercase-string when the first argument is lowercase-string.
• Str\Grapheme\before_last return null|lowercase-string when the first argument is lowercase-string.
• Str\Grapheme\before_ci return null|lowercase-string when the first argument is lowercase-string.
• Str\Grapheme\before_last_ci return null|lowercase-string when the first argument is lowercase-string.
• Str\chunk returns non-empty-list<non-empty-string> if $string is non-empty-string
• Str\chunk returns non-empty-list<non-empty-lowercase-string> if $string is non-empty-lowercase-string
• Str\Byte\chunk returns non-empty-list<non-empty-string> if $string is non-empty-string
• Str\Byte\chunk returns non-empty-list<non-empty-lowercase-string> if $string is non-empty-lowercase-string
• Str\lowercase returns non-empty-lowercase-string if $string is non-empty-string or non-falsy-string
• Str\Byte\lowercase returns non-empty-lowercase-string if $string is non-empty-string or non-falsy-string
• Str\repeat returns non-empty-lowercase-string if $string is non-empty-lowercase-string
• Str\repeat returns non-empty-string if $string is non-empty-string
• Str\repeat returns lowercase-string if $string is lowercase-string
• Str\repeat returns string(x) if $string is a literal, and $multiplier is literal, where x is the result.
• Str\slice returns lowercase-string if $string is lowercase-string
• Str\Byte\slice returns lowercase-string if $string is lowercase-string
• Str\Grapheme\slice returns lowercase-string if $string is lowercase-string
• Str\splice returns lowercase-string if $string is lowercase-string and $replacement is lowercase-string
• Str\Byte\splice returns lowercase-string if $string is lowercase-string and $replacement is lowercase-string
• Str\split returns non-empty-list<non-empty-string> if $string is non-empty-string
• Str\split returns non-empty-list<non-empty-lowercase-string> if $string is non-empty-lowercase-string
• Str\Byte\split returns non-empty-list<non-empty-string> if $string is non-empty-string
• Str\Byte\split returns non-empty-list<non-empty-lowercase-string> if $string is non-empty-lowercase-string
• Str\uppercase returns non-empty-string if $string is non-empty-string
• Str\Byte\uppercase returns non-empty-string if $string is non-empty-string

[azjezz]

cc @bendavies, hopefully this solves your issue ( and more ) :)

[azjezz]

TODO: add static analysis tests to PSL.

[bendavies]

awesome, thanks!