Remove unary + from the type system

[corollari]

Description

Remove unary + from the type system, as requested in #5470

Fixes #5470

Checklist

• Code compiles correctly
• All tests are passing
• New tests have been created which fail without the change (if possible)
• README / documentation was extended, if necessary
• Changelog entry (if change is visible to the user)
• Used meaningful commit messages

Not sure if any new test is needed, feedback would be appreciated.

[stackenbotten]

There was an error when running test_check_style for commit b51dd283de7bcbdeda85ebd78c7729a09e86d269:

Error: Trailing whitespace found:
 libsolidity/ast/Types.cpp:616: else if (_operator == Token::Sub || _operator == Token::Inc || 

Please check that your changes are working as intended.

[leonardoalt]

The unary operator tests now return:

SyntaxError: (70-72): Use of unary + is disallowed.
  TypeError: (70-72): Unary operator + cannot be applied to type uint256

If the type system disallows it, can we remove it from the syntax checker?
@chriseth @axic @bit-shift

[chriseth]

@leonardoalt I would first like to see the full test updates without removal from the syntax checker.

[chriseth]

Please also update unary_operators in SolidityExpressionCompiler.cpp

[corollari]

Working on it

[codecov]

Codecov Report

Merging #5514 into develop will decrease coverage by <.01%.
The diff coverage is 100%.

@@             Coverage Diff             @@
##           develop    #5514      +/-   ##
===========================================
- Coverage    88.12%   88.12%   -0.01%     
===========================================
  Files          324      324              
  Lines        31955    31954       -1     
  Branches      3828     3828              
===========================================
- Hits         28161    28160       -1     
  Misses        2498     2498              
  Partials      1296     1296

Flag	Coverage Δ
#all	88.12% <100%> (-0.01%)	⬇️
#syntax	28.91% <100%> (-0.01%)	⬇️

[corollari]

Done

[chriseth]

Thanks a lot!