cpp17 cleanup grammar

[guwirth]

• expr-or-braced-init-list
• simple-type-specifier
• balanced-token
• attribute ...
• nodeclspec-function-declaration
• postfix-expression
• using-declaration
• enum-head-name
• defining-type-id, defining-type-specifier, defining-type-specifier-seq
• trailing-return-type
• remove trailingTypeSpecifierSeq
• decl-specifier
• tryBlock
• functionTryBlock
• literals
• comment unqualifiedId
• comment lambdaCapture
• statement
• condition
• aliasDeclaration
• comment typeSpecifierSeq, definingTypeSpecifierSeq
• comment attributeUsingPrefix
• attributeList

mark remaining differences in CxxGrammarImpl.java

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This change is 

[guwirth]

@ALL still not all issues are solved. Remaining parts are marked with todo in grammar.
Please give us feedback to the changes.