Attach additional injected content script functions

[vovimayhem]

Currently, we inject a single function to the website when loaded as the Chrome Extension UI:

xtendize/src/ui/window-management.ts

Lines 10 to 19 in 6b25130

	async function injectContentScriptWhenReady(tabId: number, changeInfo: TabChangeInfo, tab: Tab) {
	let popUpWindowTabId = await readLocalStorage('popUpWindowTabId')
	if (tabId != popUpWindowTabId || changeInfo.status !== 'complete') return
	// Request the loaded app website to initiate the extension connection:
	return chrome.scripting.executeScript({
	target: { tabId: popUpWindowTabId },
	func: windowMessagingSetup
	})
	}

Now we need to be able to attach additional functions, specially coming from the final chrome extension code.