Enable TypeScript declaration maps

This allows go-to-definition to reach the original .ts files for
consumers of the package. It emits .d.ts.map files alongside the regular
.d.ts files

e.g. in sdk.createClient go-to-definition on createClient will place the
cursor at the function in src/matrix.ts rather than inside a definition
file lib/matrix.d.ts

Signed-off-by: Alex Macleod <alex@macleod.io>

tsconfig-build.json

@@ -1,6 +1,7 @@
 {
   "extends": "./tsconfig.json",
   "compilerOptions": {
+    "declarationMap": true,
     "sourceMap": true,
     "noEmit": false,
     "emitDecoratorMetadata": true,