[ir] Move ir to `tint::core:ir` namespace

Update the `tint::ir` namespace to the new `tint::core::ir` location.

Bug: tint:1718
Change-Id: Id64e070328732302b64f75e7c73449a12528e824
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/147020
Commit-Queue: Dan Sinclair <dsinclair@chromium.org>
Reviewed-by: Ben Clayton <bclayton@google.com>
Kokoro: Kokoro <noreply+kokoro@google.com>
diff --git a/src/tint/lang/spirv/writer/common/helper_test.h b/src/tint/lang/spirv/writer/common/helper_test.h
index 62e811c..e534c6a 100644
--- a/src/tint/lang/spirv/writer/common/helper_test.h
+++ b/src/tint/lang/spirv/writer/common/helper_test.h
@@ -81,9 +81,9 @@
     SpirvWriterTestHelperBase() : writer_(&mod, false) {}
 
     /// The test module.
-    ir::Module mod;
+    core::ir::Module mod;
     /// The test builder.
-    ir::Builder b{mod};
+    core::ir::Builder b{mod};
     /// The type manager.
     core::type::Manager& ty{mod.Types()};
 
@@ -199,7 +199,7 @@
     /// @param type the element type
     /// @param value the optional value to use
     /// @returns the scalar value
-    ir::Constant* MakeScalarValue(TestElementType type, uint32_t value = 1) {
+    core::ir::Constant* MakeScalarValue(TestElementType type, uint32_t value = 1) {
         switch (type) {
             case kBool:
                 return b.Constant(true);
@@ -218,7 +218,7 @@
     /// Helper to make a vector value with an element type of `type`.
     /// @param type the element type
     /// @returns the vector value
-    ir::Constant* MakeVectorValue(TestElementType type) {
+    core::ir::Constant* MakeVectorValue(TestElementType type) {
         switch (type) {
             case kBool:
                 return b.Composite(MakeVectorType(type), true, false);