OpenGL, OpenGL ES, and OpenGL ES-SC API and Extension Registry
You can find them in glext.h which is put out by Khronos on the official OpenGL-Registry github page. It's probably available elsewhere too but the official online OpenGL docs are kind of a zoo so I probably wouldn't waste too much time looking for them there.
Source code for Game Physics Cookbook
The other answers are correct, but there's really no particular upside to loading every OpenGL extension you want to use individually yourself. You can still use an extension loader like glad with your win32 program. Here's an example that shows when you should call gladloadgl in a win32 app
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Immediate mode 3D gizmo for scene editing and other controls based on Dear Imgui
...but if you really want to do it yourself here's an example where they do that. If you want everything it winds up being pretty long.
Multi-Language Vulkan/GL/GLES/EGL/GLX/WGL Loader-Generator based on the official specs.
With all that being said, I don't actually recommend that you do this. GLAD for example lets you select what you want to load specifically and will generate a single glad.c and glad.h pair which is very lightweight (it will also include the required Khronos headers that you'll need). If you really want you can poke around and modify these files later, but I see no reason why you wouldn't want to use it.
OGL - A Great Cross Platform OpenGL Base Library With Almost Everything OpenGL You might Ever need
17 projects | reddit.com/r/opengl | 12 Jan 2022
LearnOpenGL.com setup for Linux
1 project | reddit.com/r/u_Rapid_Movies | 9 Jan 2022
How to use OpenGL without an IDE (linking libraries)
1 project | reddit.com/r/opengl | 12 Dec 2021
How to make your own game engine (and why)
1 project | reddit.com/r/gamedev | 12 Nov 2021
Perfecting GLFW for Zig, and finding lurking undefined behavior that went unnot
3 projects | news.ycombinator.com | 31 Oct 2021