[Fuchsia] Add manifests for Cr-Fuchsia targets.

Needed since default manifest assignment will be put into the test() template in https://chromium-review.googlesource.com/c/chromium/src/+/2596114

Bug: chromium:1132878
Change-Id: I2475280c590f67cc88bcf6e877cab347079d734c
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2650765
Commit-Queue: Wez <wez@chromium.org>
Reviewed-by: Wez <wez@chromium.org>
Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Auto-Submit: Chong Gu <chonggu@google.com>
Cr-Commit-Position: refs/heads/master@{#72398}

BUILD.gn

@@ -5010,6 +5010,7 @@ if (is_fuchsia && !build_with_chromium) {
   cr_fuchsia_package("d8_fuchsia_pkg") {
     testonly = true
     binary = ":d8"
+    manifest = "//build/config/fuchsia/tests-with-exec.cmx"
     package_name_override = "d8"
   }
 

test/unittests/BUILD.gn

@@ -10,6 +10,7 @@ if (is_fuchsia) {
   cr_fuchsia_package("v8_unittests_pkg") {
     testonly = true
     binary = ":unittests"
+    manifest = "//build/config/fuchsia/tests-with-exec.cmx"
     package_name_override = "v8_unittests"
   }