windows: Configure stack size for executables (fixes issue #3250)

Change the default stack size to 8 MiB for 64-bit and 0.5 MiB for 32-bit.

CEF's main thread needs at least a 1.5 MiB stack size in order to avoid
stack overflow crashes. However, if this is set in the PE file then other
threads get this size as well, leading to address-space exhaustion in 32-bit
CEF. A new CefRunWinMainWithPreferredStackSize function uses fibers to switch
the main thread to a 4 MiB stack (roughly the same effective size as the
64-bit build's 8 MiB stack) before running any other code.

This change additionally moves the existing Windows-only functions
CefSetOSModalLoop and CefEnableHighDPISupport from cef_app.h to cef_win.h.

tests/cefclient/cefclient_win.cc

@@ -130,5 +130,22 @@ int APIENTRY wWinMain(HINSTANCE hInstance,
                       int nCmdShow) {
   UNREFERENCED_PARAMETER(hPrevInstance);
   UNREFERENCED_PARAMETER(lpCmdLine);
+
+#if defined(ARCH_CPU_32_BITS)
+  // Run the main thread on 32-bit Windows using a fiber with the preferred 4MiB
+  // stack size. This function must be called at the top of the executable entry
+  // point function (`main()` or `wWinMain()`). It is used in combination with
+  // the initial stack size of 0.5MiB configured via the `/STACK:0x80000` linker
+  // flag on executable targets. This saves significant memory on threads (like
+  // those in the Windows thread pool, and others) whose stack size can only be
+  // controlled via the linker flag.
+  int exit_code = CefRunWinMainWithPreferredStackSize(wWinMain, hInstance,
+                                                      lpCmdLine, nCmdShow);
+  if (exit_code >= 0) {
+    // The fiber has completed so return here.
+    return exit_code;
+  }
+#endif
+
   return client::RunMain(hInstance, nCmdShow);
 }