Open API for some pagefactory classes

[HlebHalkouski]

Description

Made some classes public:

• WidgetByBuilder.class,
• DefaultElementByBuilder.class,
• AppiumElementLocatorFactory.class.

If this classes made public, we adding opportunity to use AppiumElementLocatorFactory with custom decorators.

As a result, in order to accelerate develop and make UI testing more stable.

[mykola-mokhnach]

You could create a PR instead ;)