fix wrong hooks being picked for tuple types

[zerbina]

Summary

• fix tuples such as ((A, B),) and ((A,), B) being assigned the the same set of hooks
• fix the aforementioned tuples sharing the same RTTI object

Details

• add the tuple length to the type representation during type hashing (sighash), so that ((A,), B) and ((A, B),) result in two different SigHashes
• liftdestructors uses sighashes for canonicalizing structural types, thus previously treating said tuples as the same type
• RTTI creation, which also uses SigHash, was affected in the same way

[zerbina]

Prior to #1382, sighashes.hashType was also used by the C code generator for merging types, which meant that:

var x: (int, (int, int))
var y: (int, (int,), int)
y[2] = 1

resulted in a C compiler error, due to y using the same C type as x, which is:

struct tyTuple__xxx1 {
  NI Field0;
  NI Field1;
};
struct tyTuple__xxx2 {
  NI Field0;
  tyTuple__xxx1 Field1;
};

[saem]

/merge

[github-actions[bot]]

Merge requested by: @saem

Contents after the first section break of the PR description has been removed and preserved below:

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## Notes for Reviewers * a severe, long-standing issue * discovered while investigating the test failures from #1400