Operator cref node.
EBNF grammar:
cref-operator-declaration:
(cref-identifier-generic-parameters-base "." )? cref-operator-declarator
cref-operator-declarator:
cref-unary-operator-declarator
cref-binary-operator-declarator
cref-conversion-operator-declarator
cref-unary-operator-declarator:
"operator" cref-overloadable-unary-operator "(" cref-type ")"
cref-overloadable-unary-operator: one of
"+" "-" "!" "~" "++" "--" "true" "false"
cref-binary-operator-declarator:
"operator" cref-overloadable-binary-operator "(" cref-type "," cref-type ")"
cref-overloadable-binary-operator: one of
"+" "-" "*" "/" "%" "&" "|" "^" "<<" ">>" "==" "!=" ">" "<" ">=" "<="