[WIP] [Engine Details] Add details about .debugsymbols changes

[AThousandShips]

Still work in progress and waiting for the final details in:

• [Export] Linux, Windows: Support exporting with debug symbols godot#114924
• Linux, Windows: Expand .debugsymbols search in crash handler godot#122764
• [macOS] Support exporting with debug symbols. godot#122874

As well as a future macOS PR, and a possible future PR to integrate downloading debug symbols in the template manager

Not sure exactly where to detail this but I've added notes to the areas where it makes sense to me to place notes. Not sure about the best scope for this but will focus on the distribution and compilation details for now, might be good to add a note in the scripting/debug section as well as a follow-up for general crash handling but I think that's out of scope for this

Much of the specifics of the templates and the export process are in the respective export plugin pages (linked at the bottom of each Exporting For page) so currently not planning to add anything there to reduce duplication

Currently this is limited to a minor correction to the documentation I found when I was looking at what documentation already existed in preparation for making this PR.

Todo:

• Consider additional areas to change
• Document the general build instructions for debug symbols
• Document the Windows build instructions
• Document the Linux build instructions
• Document the macOS build instructions
• Document template download manager changes (if relevant)