lang/go127: Add go 1.27

Changes:
  Go 1.27 now supports generic methods: a method declaration may declare
  its own type parameters. This widely anticipated change allows adding
  generic functions within the namespace of a particular data type where
  before one had to declare such functions with a scope of the entire
  package.

  A key in a struct literal may now be any valid field selector for the
  struct type, not just a (top-level) field name of the struct.

  Function type inference has been generalized to apply in all contexts
  where a generic function is assigned to a variable of (or converted
  to) a matching function type.