[DOCS] New guidelines for referencing and linking to source code

[willihay]

Describe the issue briefly

There's nothing in the Contributor Style Guide as of yet regarding a standard format for references and links to O3DE source code. Contributors have used a variety of formats in the O3DE User Guide. To promote consistency, we should provide some guidelines in the Contributor Guide.

Which page(s) / section(s) are affected?

Links style

In this section on Formatting, various styles for links are presented. I recommend that we divide this into Docs links - which would contain the styles currently mentioned - and Source code links. Under source code links, I recommend the following guidelines:

New guideline on source code links

When linking to specific files or line numbers in source code, use permalinks whenever possible.

File link example:

[Gems/StartingPointInput/Code/Source/StartingPointInputGem.cpp](https://github.com/o3de/o3de/blob/14c366cabc906ac1367492c457959333c2eaafc5/Gems/StartingPointInput/Code/Source/StartingPointInputGem.cpp)

Result:

Gems/StartingPointInput/Code/Source/StartingPointInputGem.cpp

To link to a specific section of the source file, such as a function or a line of code, include line numbers in the URL. It's preferable to describe the section using words instead of line numbers because line numbers can easily change. While a permalink will always be valid, a line number range in the link label can be misleading if those lines have changed in more recent versions of the source code.

File section link example:

[Reflect function calls in Gems/StartingPointInput/Code/Source/StartingPointInputGem.cpp](https://github.com/o3de/o3de/blob/14c366cabc906ac1367492c457959333c2eaafc5/Gems/StartingPointInput/Code/Source/StartingPointInputGem.cpp#L118-L122)

Result:

Reflect function calls in Gems/StartingPointInput/Code/Source/StartingPointInputGem.cpp

To obtain permalinks for a file in a GitHub repo, navigate to the Code tab and open the file, then choose Copy permalink from the ... menu:

To obtain permalinks for specific lines of code in a file in a GitHub repo:

1. Navigate to the Code tab and open the file.
2. Click on the first line number in the block.
3. Shift+click on the last line number in the block.
4. Choose Copy permalink from the ... menu to the left of the first line number:

Alternatively, you can just manually add the line number range to the end of the file's permalink URL, using the format: #Lnnn-Lnnn, where nnn represents a line number.

[willihay]

Issue created from discussion o3de/sig-docs-community#47