chore(core): augmentations should use relative import (#26364)

Previously (accidentally) used the module name as a name for the import. This caused the build to fail with `error TS5055: Cannot write file 'aws-cdk-lib/aws-cloudwatch/index.d.ts' because it would overwrite input file.` Also exclude declaration files from the build, which makes it slightly faster (~20s).

----

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Author: mrgrain

packages/aws-cdk-lib/package.json

@@ -66,7 +66,8 @@
   },
   "jsii": {
     "excludeTypescript": [
-      "scripts"
+      "scripts",
+      "**/*.d.ts"
     ],
     "outdir": "dist",
     "targets": {

tools/@aws-cdk/spec2cdk/lib/cfn2ts/index.ts

@@ -157,6 +157,7 @@ export async function generateAll(
       importLocations: {
         core: options.coreImport,
         coreHelpers: `${options.coreImport}/lib/helpers-internal`,
+        cloudwatch: options.cloudwatchImport,
       },
     },
   );