Swift SIL: escape effects for function arguments.

Store a list of argument effects in a function, which specify if and how arguments escape.
Such effects can be specified in the Swift source code (for details see docs/ReferenceGuides/UnderscoredAttributes.md) or derived in an optimization pass.

For details see the documentation in SwiftCompilerSources/Sources/SIL/Effects.swift.

utils/gyb_syntax_support/AttributeNodes.py

@@ -66,6 +66,10 @@ ATTRIBUTE_NODES = [
                              kind='DerivativeRegistrationAttributeArguments'),
                        Child('NamedAttributeString',
                              kind='NamedAttributeStringArgument'),
+                       # TokenList for custom effects which are parsed by
+                       # `FunctionEffects.parse()` in swift.
+                       Child('TokenList', kind='TokenList',
+                             collection_element_name='Token'),
                    ], description='''
                    The arguments of the attribute. In case the attribute
                    takes multiple arguments, they are gather in the