fix(metro-serializer-esbuild): enable esbuild sourcemap

[tido64]

Description

esbuild's sourcemap will be mapped to the transformed JS. Ideally, it should map to the original source code, but since Metro currently handles the transformation, we cannot do that. At least now, it won't be pointing at wrong lines.

Test plan

1. Build everything up to, and including, @rnx-kit/test-app:

   yarn
   yarn build-scope @rnx-kit/test-app
   

2. Enable experimental_treeShake:

   diff --git a/packages/test-app/package.json b/packages/test-app/package.json
   index a870cbb..7a3438b 100644
   --- a/packages/test-app/package.json
   +++ b/packages/test-app/package.json
   @@ -68,7 +68,7 @@
            ]
          },
          "typescriptValidation": true,
   -      "experimental_treeShake": false,
   +      "experimental_treeShake": true,
          "targets": [
            "android",
            "ios",

3. Run yarn bundle+esbuild
4. Examine dist/main+esbuild.*.jsbundle.map