Attribute section AST node.
EBNF grammar:
attribute-section:
"[" ( attribute-target-specifier )? attribute-list "]"
"[" ( attribute-target-specifier )? attribute-list "," "]"
attribute-target-specifier:
attribute-target ":"
attribute-target:
"field"
"event"
"method"
"param"
"property"
"return"
"type"