Replace vendored SIMD Everywhere by prefix/system install

[tytan652]

Description

[!IMPORTANT]
Depends on:

• https://github.com/obsproject/obs-deps/pull/255
• ~~Drop of the CMake legacy (I can implement legacy path if really needed)~~

Close https://github.com/obsproject/obs-studio/pull/5067

Replace vendored SIMD Everywhere by prefix/system install.

SIMD Everywhere finder needs to be installed alongside libobs CMake package since its headers depends on it.

macOS AVX intrinsics is included to make sure that AVX defines are present.

Motivation and Context

Reduce in-tree vendored deps in OBS Studio repo.

How Has This Been Tested?

Build in CI on my fork.

Types of changes

• Code cleanup (non-breaking change which makes code smaller or more readable)

Checklist:

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