Add Ractor.shareable_proc and Ractor.shareable_lambda

No test added since the spy implementation makes blocks unshareable.

Author: soutaro

core/ractor.rbs

@@ -380,6 +380,36 @@ class Ractor
   #
   def self.shareable?: (untyped obj) -> bool
 
+  # <!--
+  #   rdoc-file=ractor.rb
+  #   - Ractor.sharable_proc(self: nil){} -> sharable proc
+  # -->
+  # It returns shareable Proc object. The Proc object is shareable and the self in
+  # a block will be replaced with the value passed via `self:` keyword.
+  #
+  # In a shareable Proc, you can not access to the outer variables.
+  #
+  #     a = 42
+  #     Ractor.shareable_proc{ p a }
+  #     #=> can not isolate a Proc because it accesses outer variables (a). (ArgumentError)
+  #
+  # The `self` should be a sharable object
+  #
+  #     Ractor.shareable_proc(self: self){}
+  #     #=> self should be shareable: main (Ractor::IsolationError)
+  #
+  def self.shareable_proc: [T] () { (?) [self: nil] -> T } -> ^(?) [self: nil] -> T
+                         | [T, S] (self: S) { (?) [self: S] -> T } -> ^(?) [self: S] -> T
+
+  # <!--
+  #   rdoc-file=ractor.rb
+  #   - Ractor.sharable_proc{} -> sharable proc
+  # -->
+  # Same as Ractor.sharable_proc, but returns lambda proc.
+  #
+  def self.shareable_lambda: [T] () { (?) [self: nil] -> T } -> ^(?) [self: nil] -> T
+                           | [T, S] (self: S) { (?) [self: S] -> T } -> ^(?) [self: S] -> T
+
   # <!--
   #   rdoc-file=ractor.rb
   #   - Ractor.store_if_absent(key){ init_block }