* ConcatAnalyzer improvements.
Deduplicate code.
Improve type inference.
Allow literal type inference when only one side has multiple types (fixes#5483).
Fix invalid type inference with negative int as right operand.
* Fix inference to be lowercase-string when concatenating int.
* Fix TNonEmptyLowercaseString to not be subtype of TNonFalsyString.
'0' is a non-empty-lowercase-string that is falsy.
* Fix other issues with non-falsy-string.
* Nest ands and ors
Co-authored-by: Matthew Brown <github@muglug.com>