[tint] Namespace the strconv files

This cl moves the utils/strconv files into tint::strconv. The `std::endls` are converted to `\n` which follows the recommendations from the cpp core guidelines.

Bug: tint:1988
Change-Id: Ie3522e5fe774abc392eea31e7ef5fcd7e9be624a
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/160861
Reviewed-by: Ben Clayton <bclayton@google.com>
Kokoro: Kokoro <noreply+kokoro@google.com>
Commit-Queue: dan sinclair <dsinclair@chromium.org>

src/tint/utils/cli/cli.h

diff --git a/src/tint/utils/cli/cli.h b/src/tint/utils/cli/cli.h
index b315884..b0e89e4 100644
--- a/src/tint/utils/cli/cli.h
+++ b/src/tint/utils/cli/cli.h
@@ -282,13 +282,13 @@
         auto arg = arguments.front();
 
         if constexpr (is_number) {
-            auto result = ParseNumber<T>(arg);
+            auto result = strconv::ParseNumber<T>(arg);
             if (result) {
                 value = result.Get();
                 arguments.pop_front();
                 return Success;
             }
-            if (result.Failure() == ParseNumberError::kResultOutOfRange) {
+            if (result.Failure() == strconv::ParseNumberError::kResultOutOfRange) {
                 return ErrInvalidArgument(arg, "value out of range");
             }
             return ErrInvalidArgument(arg, "failed to parse value");