feat(inspector): serve source maps to DevTools via Network.loadNetworkResource

Chrome DevTools no longer fetches external source maps itself when
debugging remote targets: it issues Network.loadNetworkResource to the
target and reads the result back through IO.read/IO.close. None of these
embedder-side CDP domains are implemented by V8's inspector, so external
source maps failed and apps had to fall back to bloated
inline-source-map builds.

- Handle Network.loadNetworkResource natively: resolve the URL back to a
  file on disk and reply with a stream handle (success:false +
  net::ERR_FILE_NOT_FOUND when missing).
- Implement IO.read (1MB base64 chunks; eof only on a final empty read,
  since the frontend discards data accompanying eof) and IO.close.
- Reply with a JSON-RPC error for unsupported schemes (e.g. https) so
  DevTools keeps its existing fallback of fetching from the host.
- Rewrite sourceMapURL in outgoing Debugger.scriptParsed /
  Debugger.scriptFailedToParse events from relative/file:// URLs to a
  custom nsruntime:// scheme. DevTools hard-excludes file:, data: and
  devtools: URLs from loading through the target, so without the rewrite
  it would never send Network.loadNetworkResource and instead try (and
  fail) to read device files from the host machine. data: and http(s)
  URLs are left untouched, keeping inline source maps working.
- Allow opting out via nativescript.config.ts:
  android.disableSourceMapURLRewrite (or the same key at the top level).
- Serve these messages on the websocket read thread (new native
  handleMessageOnSocketThread), since the main-thread queue is
  unavailable exactly when DevTools needs source maps: the pause loop
  bypasses dispatchMessage and a busy isolate never drains the queue.
  The handler is V8-free and returns the response for Java to send on
  the receiving socket.
- Make Debugger.pause interrupt busy JS via Isolate::RequestInterrupt,
  skipped while already paused in the nested loop to avoid a spurious
  re-pause after resume.
- Vendor nlohmann/json v3.12.0 (third_party/json.hpp, header-only) for
  CDP message handling outside V8.

Ports NativeScript/ios#385 and NativeScript/ios#378 to Android.

Refs: nodejs/node#58077

Author: edusperoni

test-app/app/src/main/java/com/tns/AndroidJsV8Inspector.java

@@ -37,6 +37,8 @@ class AndroidJsV8Inspector {
 
     protected native final void dispatchMessage(String message);
 
+    private native String handleMessageOnSocketThread(String message);
+
     private Handler mainHandler;
 
     private final Object debugBrkLock;
@@ -294,6 +296,22 @@ protected void onMessage(final NanoWSD.WebSocketFrame message) {
                 Log.d("V8Inspector", "To dbg backend: " + message.getTextPayload() + " ThreadId:" + Thread.currentThread().getId());
             }
 
+            // Network.loadNetworkResource / IO.read / IO.close are served from
+            // disk on this thread so source maps load even while the isolate is
+            // paused at a breakpoint or busy running JS; Debugger.pause schedules
+            // a V8 interrupt and still flows through the queue.
+            String fastPathResponse = handleMessageOnSocketThread(message.getTextPayload());
+            if (fastPathResponse != null) {
+                try {
+                    send(fastPathResponse);
+                } catch (IOException e) {
+                    if (com.tns.Runtime.isDebuggable()) {
+                        e.printStackTrace();
+                    }
+                }
+                return;
+            }
+
             inspectorMessages.offer(message.getTextPayload());
 
             if (!AndroidJsV8Inspector.ReadyToProcessMessages.get()) {