fix(android): call WebView.stopLoading() from main thread

[garymathews]

• Allow Titanium.UI.WebView.stopLoading() to function when called from events

TEST CASE

const win = Ti.UI.createWindow();
const webView = Ti.UI.createWebView({ url: 'https://google.com/' });

webView.addEventListener('beforeload', e => {
    webView.stopLoading();
});

win.add(webView);
win.open();

JIRA Ticket

[build]

	Messages
📖	💾 Here's the generated SDK zipfile.
📖	✅ All tests are passing Nice one! All 4336 tests are passing. (There are 471 tests skipped)
📖	✊ The commits in this PR match our conventions! Feel free to Rebase and Merge this PR when ready.

Generated by 🚫 dangerJS against b268be7

[sgtcoolguy]

Pinging @jquick-axway for CR since he had already had some feedback/discussion on the closed 8_1_X backport at #11171

[ssekhri]

FR passed.
Verified on:
Mac OS 10.14.6
Ti SDK: 8.3.0.v20190910145509
Appc CLI: 7.1.1
Node: 10.5.0
JDK: 10.0.2
Studio: 5.1.4.201909061933
Device: Nexus 4(5.1.1), Android emulator (v8.0)

[ssekhri]

Waiting for CR @jquick-axway

[jquick-axway]

CR: Pass