Clean up and fixes to "How Flutter works"

[parlough]

• Adds an accurate description to the page.
• Updates the headings to be more interesting and flow more naturally (Please do review and provide feedback here). Also add shorter fragment IDs to each heading.
• Wrap the youtube embeds for better styling and with a max width for better spacing.
• Adds a next card so developers know where to go to continue their learning journey.
• Uses code font in the video descriptions where appropriate.
• Switches to non-code version of "render objects" and similar where it makes sense, particularly when talking about multiple instances.
• Removes some usages of "we" from the descriptions.
• Slightly cleans up and updates some copy.

[gemini-code-assist]

Code Review

This pull request provides a good cleanup and set of fixes for the 'How Flutter works' page. The descriptions are more accurate, the headings are more engaging, and the new styling for video embeds improves the layout. Using code fonts for technical terms is a great readability improvement. I've found one minor grammatical issue in the updated content and suggested a correction.

[flutter-website-bot]

Visit the preview URL for this PR (updated for commit 0ef421b):

https://flutter-docs-prod--pr13172-fix-how-flutter-works-ivdzf4f2.web.app