Use a context object instead of a singleton

This Cl replaces the TypeManager singleton with a context object.

Bug: tint:29
Change-Id: Ia662709db1b562c34955633977ce4363f28f238e
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/17780
Reviewed-by: David Neto <dneto@google.com>
diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 6a4ed6e..70979a2 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -387,6 +387,7 @@
     reader/wgsl/parser_impl_switch_body_test.cc
     reader/wgsl/parser_impl_switch_stmt_test.cc
     reader/wgsl/parser_impl_test.cc
+    reader/wgsl/parser_impl_test_helper.h
     reader/wgsl/parser_impl_type_alias_test.cc
     reader/wgsl/parser_impl_type_decl_test.cc
     reader/wgsl/parser_impl_unary_expression_test.cc