[docs, tools] Add 3rd party links, debug and testing guidelines; add extra tools for maintaining strings, rewrite lanczos generator in perl (#2749)

RenderDoc checklist inspired by writeup of Charles G. of LunarG
Signed-off-by: lizzie <lizzie@eden-emu.dev>

Reviewed-on: https://git.eden-emu.dev/eden-emu/eden/pulls/2749
Reviewed-by: MaranBr <maranbr@eden-emu.dev>
Co-authored-by: lizzie <lizzie@eden-emu.dev>
Co-committed-by: lizzie <lizzie@eden-emu.dev>

docs/User.md

@@ -8,3 +8,4 @@ This handbook is primarily aimed at the end-user - baking useful knowledge for e
 - **[Audio](user/Audio.md)**
 - **[Graphics](user/Graphics.md)**
 - **[Platforms and Architectures](user/Architectures.md)**
+- **[Testing](user/Testing.md)**