Allow esbuild options to be configured in Worker runtime

[lucassarcanjo]

Previously, KeepNames, Target, and Sourcemap options were hardcoded and ignored user configuration. This allows users to override these options via transform.server.build.esbuild to resolve issues like SSR hydration problems in TanStack Start applications.

Note: KeepNames defaults to true. Only override if user explicitly disables it. For Target and Sourcemap, check non-zero values as zero represents "not set" for these enums.

Fixes #6293

[vimtor]

thanks for your contribution @lucassarcanjo

do you have any good example/use case for me to try this out?

[lucassarcanjo]

I used examples/cloudflare-worker and added custom properties like keepNames in the build configuration:

Example of sst.config.ts

/// <reference path="./.sst/platform/config.d.ts" />

export default $config({
app(input) {
  return {
    name: "cloudflare-worker",
    removal: input?.stage === "production" ? "retain" : "remove",
    home: "cloudflare",
  };
},
async run() {
  const bucket = new sst.cloudflare.Bucket("MyBucket");
  const worker = new sst.cloudflare.Worker("MyWorker", {
    handler: "./index.ts",
    link: [bucket],
    url: true,

    // configuration to be tested here
    build: {
      esbuild: {
        keepNames: false,
      },
    },
  });

  return {
    api: worker.url,
  };
},
});

Added a log to get all configurations from worker.go and got the correct values:

slog.Info("building with options", "options", options)

[vimtor]

thanks for your contribution @lucassarcanjo

the keepNames option works without any issue

however the sourcemap and target options don't seem to update when you set the config probably because of how the json unmarshalling works from the raw string to the go enum

we either fix them or remove their overriding