Restore "MSL writer: make signed int overflow defined behaviour"

This reverts commit e33b0baa08.

Added tests/expressions/literals/intmin.wgsl test.

Bug: tint:124
Change-Id: I3d46f939ff20fa377ddb5fcb52f9afe728b8e430
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/60441
Kokoro: Kokoro <noreply+kokoro@google.com>
Commit-Queue: Antonio Maiorano <amaiorano@google.com>
Reviewed-by: Ben Clayton <bclayton@google.com>
Reviewed-by: David Neto <dneto@google.com>

test/expressions/binary/left-shift/scalar-scalar/u32.wgsl

@@ -0,0 +1,6 @@
+[[stage(compute), workgroup_size(1)]]
+fn f() {
+    let a = 1u;
+    let b = 2u;
+    let r : u32 = a << b;
+}