Deprecate Kernel#Namespace

Namespace functionality will be added in Ruby4.
If added, `Namespace()` is likely to create confusion.

Author: ksss

lib/rbs/namespace.rb

@@ -119,6 +119,7 @@ def ascend
 
 module Kernel
   def Namespace(name)
+    warn "Kernel#Namespace() is deprecated. Use RBS::Namespace.parse instead.", category: :deprecated
     RBS::Namespace.parse(name)
   end
 end

sig/namespace.rbs

@@ -141,7 +141,6 @@ module RBS
 end
 
 module Kernel
-  # Parses given string and returns Namespace.
-  #
-  def Namespace: (String) -> RBS::Namespace
+  # Deprecated: Use `RBS::Namespace.parse` instead
+  %a{steep:deprecated} def Namespace: (String) -> RBS::Namespace
 end

test/rbs/signature_parsing_test.rb

@@ -2153,7 +2153,7 @@ class Foo
         end
 
         use.clauses[1].tap do |clause|
-          assert_equal Namespace("RBS::AST::Declarations::"), clause.namespace
+          assert_equal RBS::Namespace.parse("RBS::AST::Declarations::"), clause.namespace
           assert_equal "RBS::AST::Declarations::", clause.location[:namespace].source
           assert_equal "*", clause.location[:star].source
         end

test/rbs/use_map_test.rb

@@ -36,7 +36,7 @@ def test_import_single_clause
   end
 
   def test_import_wildcard_clause
-    map.build_map(Use::WildcardClause.new(namespace: Namespace("Foo::"), location: nil))
+    map.build_map(Use::WildcardClause.new(namespace: RBS::Namespace.parse("Foo::"), location: nil))
 
     assert_equal TypeName("::Foo::M"), map.resolve?(TypeName("M"))
     assert_equal TypeName("::Foo::_I"), map.resolve?(TypeName("_I"))