Restructure & add pre-built examples

[ellahathaway]

Related to #3358 (comment)

This PR aims to improve the readability and usability of the pre-built elimination document. It accomplishes the following:

• Improve the document's readability and usability by providing clear, step-by-step instructions on how to handle new dependencies and pre-builts in the source-build process.
• The document now explicitly lists the possible actions that a developer might need to take, such as updating versions of certain packages, modifying Version.Details.xml and Versions.Props files, and adding new packages to the source-build-reference-packages or source-build-externals repositories.
• Each action is explained in detail, with specific examples given. This makes it easier for developers to understand what they need to do and how to do it.
• The document also provides links to additional resources, such as the source-build-reference-packages and source-build-externals repositories, which can provide further information and context.
• The document mentions the importance of comparing against SourceBuildPrebuiltBaseline.xml file.
• Splits important information into separate paragraphs and sections to effectively point readers to key information and allow readers to quickly identify what they need to do.

These formatting changes, along with the content updates, make the document more user-friendly and accessible to developers of different experience levels.

[dotnet-issue-labeler]

I couldn't figure out the best area label to add to this PR. If you have write-permissions please help me learn by adding exactly one area label.

[mthalman]

@ViktorHofer - I've added you as a review as you encounter prebuilts fairly often. It'd be good to get your perspective since the intention is that you'd be able to follow these instructions to resolve such issues on your own.

[ViktorHofer]

Don't have time to review right now but will take a look over the weekend or on Monday.

[MichaelSimons]

Ella, Thanks for improving this documentation!

[ellahathaway]

@ViktorHofer - Requesting review since I've now updated 'new-dependencies.md' As Matt mentioned in a previous comment, your perspective is important since we intend for readers to be able to follow the instructions and resolve issues on their own. Thanks in advance!