feat: add thumbSize to set size of thumb

[bdtren]

Summary:

This PR adds a new thumbSize prop to control the thumb’s size for both with and without thumb image. It is a simple feature that I need and did patch-package in some of my projects but I didn't have a chance to contribute, I think some developers might also need it:

Android	iOS

Test Plan:

• Install/refresh package:

npm install
npm run refresh-package

• Android:

npm run example-android

Verify in the example list:
“Custom thumb size (no image)” renders a larger thumb (e.g. thumbSize={32}) tinted with thumbTintColor.
“Custom thumb size (scaled image)” renders the thumb image scaled to the configured size (e.g. thumbSize={60}).

• iOS:

npm run example-ios

Verify the same two examples behave equivalently on iOS (thumb resizes; image scales when provided).

[BartoszKlonowski]

So far I have some cosmetic comments and a question before I'll dive deeper into the implementation itself.

[BartoszKlonowski]

Hello @bdtren, let me know please if you plan to push this forward, or should I take it from here?

[bdtren]

Hi @BartoszKlonowski ,
Oh, my apologies, I didn't know you guys are reviewing my PR, let me check...

[bdtren]

Hi @BartoszKlonowski ,
I just updated the code and change the function name to refreshThumb, it need to trigger all the time to prevent other thumb setting become wrong when one of thumbSize, thumbImage or thumbImage changed. Please check it, thanks!