* many bugfixes for js
fixes#12672, fixes#14153, closes#14123, closes#11331, fixes#11783, fixes#13966, fixes#14087, fixes#14117, closes#12256.
mostly fixes the fact that it was allowed to assign to newly created temp variables. additionally attempts to get rid of null initialized seqs/strings (though they might pop up here and there); this simplifies a lot of things and makes code size smaller. even if null seqs/strings pop up here and there it's still better than all those bugs existing.
* formatting fixes
* CI fixes
* more CI fixes
* proper indentation for the generated JS code
* improved dead-code elimination for JavaScript
* test the JS dead-code elimination
A new test spec has been added - "maxcodesize". It specifies the
maximum size of the generated code in bytes.
