Rename 'intrinsic' to 'builtin'

This matches the term used in the WGSL spec.

Change-Id: I4603332b828450c126ef806f1064ed54f372013f
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/78787
Reviewed-by: James Price <jrprice@google.com>
Kokoro: Kokoro <noreply+kokoro@google.com>

test/unittest/reader/spirv/SpvLogicalTest_IsNan_Vector.spvasm.expected.hlsl

@@ -1,6 +1,6 @@
 SKIP: FAILED
 
-warning: use of deprecated intrinsic
+warning: use of deprecated builtin
 void main_1() {
   const bool2 x_1 = isnan(float2(50.0f, 60.0f));
   return;