Change macOS requirements from macOS 10.15 to macOS 12

[cpaulgilman]

Describe the bug

SAM does not run on macOS 10.15 Catalina. The SAM Downloads page says the minimum version is 10.15.

Running otool -l -arch x86_64 SAM.app/Contents/Frameworks/ssc.dylib in a terminal from the /Applications/SAM_2023.12.17 folder results in the following, indicating that LHS requires macOS 10.17:

According to the Wikipedia article on macOS versions, the oldest version still receiving updates from Apple is macOS 12 Monterrey.

To Reproduce

1. Start SAM on a Mac running macOS 10.15 Catalina.

Proposed Solution

Change the minimium requirement to macOS 12 Monterrey. Requires updating CMake, GitHub CI, etc.

SAM Downloads page description updated for Mac version 3/19/2024.