cmake: Fix default installation directory for Windows

[sorayuki]

Description

Fix the wrong default value in cmake script.

Motivation and Context

The default installation for Windows in cmake script is wrong. OBS won't load plugin from there.

from

https://github.com/obsproject/obs-studio/blob/31.0.1/UI/window-basic-main.cpp#L201
int ret = GetProgramDataPath(base_module_dir, sizeof(base_module_dir), "obs-studio/plugins/%module%");
https://github.com/obsproject/obs-studio/blob/31.0.1/UI/window-basic-main.cpp#L211
string path = base_module_dir;
https://github.com/obsproject/obs-studio/blob/31.0.1/UI/window-basic-main.cpp#L231
obs_add_module_path((path + "/bin/64bit").c_str(), (path + "/data").c_str());

How Has This Been Tested?

My plugin works.

Types of changes

Bug fix

Checklist:

• My code has been run through clang-format.
• I have read the contributing document.
• My code is not on the master branch.
• The code has been tested.
• All commit messages are properly formatted and commits squashed where appropriate.
• I have included updates to all appropriate documentation.

[RytoEX]

Nit: please capitalize "Fix" in your commit message and PR title.

[PatTheMav]

This change is correct insofar as the directories are mapped as follows:

APPDATA         <-> CSIDL_APPDATA
ALLUSERSAPPDATA <-> CSIDL_COMMON_APPDATA

OBS Studio uses CSIDL_COMMON_APPDATA as the "program path", so CMake code has to use the corresponding environment variable.