VM: fix some bugs from JSON tests

[fyrchik]

• fail if NIP, (X)DROP, ROT or EQUAL have not enough arguments.
• fail if XTUCK argument is 0
• PICKITEM should accept bytearrays
• NEWARRAY/NEWSTRUCT should create array of BoolItem{false} items instead of nils
• REMOVE should return value of the same type as the argument (do not perform Struct -> Array conversion)
• PUSH0 should push empty byte array (it is converted when 0 is needed)
• NEWARRAY can accept []byte operand. Common usecase: PUSH0, NEWARRAY
• SIZE can accept any argument castable to ByteArray
• SHL/SHR do not change type of the operand if shift is by 0 (if applied to bytearray, leave bytearray as it is).

There are to more bugs specified in #196 . They include using Array as a pointer value and can me more prone to hidden bugs, so I will do this separately.

There are some tests in pkg/vm/tests/ which fail. I am not sure if tests or codegen should be fixed. E.g. if user is expecting Integer we could emit PUSH0, ADD on top of []byte item to return Integer. Or just make tests expect []byte{0}. All this implicit conversions stuff is rather annoying both from user's and developer's point of view.

[roman-khimov]

Looks like we have the same problem as in ca10fb0 with REVERSE.

[roman-khimov]

There are some tests in pkg/vm/tests/ which fail

And BTW, we need to fix them one way or another before this merge.

[codecov]

Codecov Report

Merging #394 into master will increase coverage by 0.43%.
The diff coverage is 78.78%.

@@            Coverage Diff             @@
##           master     #394      +/-   ##
==========================================
+ Coverage   49.91%   50.34%   +0.43%     
==========================================
  Files          81       80       -1     
  Lines        5469     5430      -39     
==========================================
+ Hits         2730     2734       +4     
+ Misses       2484     2446      -38     
+ Partials      255      250       -5

Impacted Files	Coverage Δ
pkg/vm/compiler/analysis.go	72.88% <100%> (ø)	⬆️
pkg/vm/stack.go	87.5% <100%> (+1.78%)	⬆️
pkg/vm/compiler/codegen.go	68.31% <40%> (ø)	⬆️
pkg/vm/vm.go	67.53% <84.61%> (+5.83%)	⬆️
pkg/core/storage/boltdb_store.go
pkg/core/storage/store.go	40.9% <0%> (+3.4%)	⬆️

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[fyrchik]

There are some tests in pkg/vm/tests/ which fail

And BTW, we need to fix them one way or another before this merge.

I have added []byte{} in tests for now. In the future it is better to modify tests to support weak equality comparison or indeed change codegen.

[roman-khimov]

2ef8145 does more than it's written in the commit message, you should also mention changes made wrt type handling changes.

[roman-khimov]

46c56d1 should be squashed with c28c798, otherwise you have tests failing inbetween these commits.

[roman-khimov]

Please, also fix REVERSE behavior to not push the result to the stack, it's the only one left with this bug after the current patchset.