intrinsics: Add new struct form of modf(), frexp()

Implement these for all the writers.
SPIR-V reader not implemented (the old overloads weren't implemented either).

Deprecate the old overloads.

Fixed: tint:54
Change-Id: If66d26dbac3389ff604734f31b426abe47868b91
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/59302
Kokoro: Kokoro <noreply+kokoro@google.com>
Reviewed-by: James Price <jrprice@google.com>
diff --git a/test/intrinsics/gen/modf/5e8476.wgsl.expected.hlsl b/test/intrinsics/gen/modf/5e8476.wgsl.expected.hlsl
index 8fabfe2..dbe27e6 100644
--- a/test/intrinsics/gen/modf/5e8476.wgsl.expected.hlsl
+++ b/test/intrinsics/gen/modf/5e8476.wgsl.expected.hlsl
@@ -1,3 +1,7 @@
+intrinsics/gen/modf/5e8476.wgsl:29:18 warning: use of deprecated intrinsic
+  var res: f32 = modf(1.0, &arg_1);
+                 ^^^^
+
 static float arg_1 = 0.0f;
 
 void modf_5e8476() {