RNMobile: Fix links, images, and formatting in documentation

[guarani]

Description

This fixes a couple of issues in Native Mobile docs (especially when viewed from the Block Editor Handbook):

• Some doc links were broken because they used relative paths to files outside of the docs folder, others likely because files had been renamed and links were not updated
• An image was broken because it didn't use an absolute link but instead used a relative link
• Code snippets needed to be indented properly
• Code snippets were missing a language specifier – adding this fixes their formatting, especially in the Block Editor Handbook

How has this been tested?

• Test changes by viewing the changed files on the latest commit on this branch and verify links, images, and formatting look correct
• (After merging and waiting 15 minutes for the Block Editor Handbook to sync) Open the Block Editor Handbook to the relevant files changes here and verify all links, images and formatting look correct

Types of changes

• Documentation updates

Checklist:

• My code is tested.
• My code follows the WordPress code style.
• My code follows the accessibility standards.
• I've tested my changes with keyboard and screen readers.
• My code has proper inline documentation.
• I've included developer documentation if appropriate.
• I've updated all React Native files affected by any refactorings/renamings in this PR (please manually search all *.native.js files for terms that need renaming or removal).

[mchowning]

Everything looks good. Thanks for the 🧹 @guarani !