docs: Fix typos, code examples, and other inconsistencies in Native Development section

[amandeepmittal]

Why

After reviewing documents under "Native Development" section, I found a few inconsistencies and typos.

How

This PR:

• Fixes the typos in code examples and the rest of the text for docs under Native Development section
• Fixes minor formatting issues (such as using a period in a section heading)
• Adds missing file titles for code in Cross-Platform with C++ guide
• Updates commands for generating Pods in Cross-Platform with C++ guide with copy/pastable code blocks; this makes it consistent with the previous guide to perform the same step
• Adds a missing command to create a new project in Modules > Android and iOS
• Fixes the order of screenshots in Modules > Android and iOS > Step 4 Write your native Platform code > iOS (image 4 is used twice and image 6 was missing)

cc: @blakef

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[Simek]

Thanks for the updates, LGTM! 👍

[blakef]

Thank you for this. Much appreciated!