[compiler] Enable sourceMaps in tsconfig (#30064)

With this, we can set a `debugger` breakpoint and we'll break into the
source code when running tests with snap. Without this, we'd break into
the transpiled js code.

Author: gsathya

compiler/packages/snap/src/runner-watch.ts

@@ -27,7 +27,7 @@ export function watchSrc(
   const host = ts.createWatchCompilerHost(
     configPath,
     ts.convertCompilerOptionsFromJson(
-      { module: "commonjs", outDir: "dist" },
+      { module: "commonjs", outDir: "dist", sourceMap: true },
       "."
     ).options,
     ts.sys,