all: replace target=wasi with target=wasip1

This eliminates the 'wasi' build tag in favor of 'GOOS=wasip1', introduced in Go 1.21.

For backwards compatablity, -target=wasi is a synonym for -target=wasip1.

src/testing/is_wasi_no_test.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 //
-//go:build !wasi && !wasip1
+//go:build !wasip1
 
 package testing_test
 

src/testing/is_wasi_test.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 //
-//go:build wasi || wasip1
+//go:build wasip1
 
 package testing_test