feat: Add option to conditionally disable site instance patches (#18396)

* chore: allow conditional disable of the site instance override patches at runtime

* feat: add app.allowRendererProcessReuse property to allow runtime disable of site instance overrides

spec: add tests for the new allowRendererProcessReuse property

feat: add console warnings / errors for loading non context-aware native modules
  * Only error if the patch is disabled
  * Warn all the time, this will ship in Electron 7

spec/fixtures/api/site-instance-overrides/main.js

@@ -0,0 +1,33 @@
+const { app, BrowserWindow, ipcMain } = require('electron')
+const path = require('path')
+
+process.on('uncaughtException', (e) => {
+  console.error(e)
+  process.exit(1)
+})
+
+app.allowRendererProcessReuse = JSON.parse(process.argv[2])
+
+const pids = []
+let win
+
+ipcMain.on('pid', (event, pid) => {
+  pids.push(pid)
+  if (pids.length === 2) {
+    console.log(JSON.stringify(pids))
+    if (win) win.close()
+    app.quit()
+  } else {
+    if (win) win.reload()
+  }
+})
+
+app.whenReady().then(() => {
+  win = new BrowserWindow({
+    show: false,
+    webPreferences: {
+      preload: path.resolve(__dirname, 'preload.js')
+    }
+  })
+  win.loadFile('index.html')
+})