* Update the minimum CMake version to 3.20
Sets the cmake_minimum_required calls to version 3.20 and updates the
README.md to point at the general CMake download page instead of a stale
link.
* Remove unnecessary cmake minimum version
It was using an old 3.0 version and can be removed.
* Additional updates to CMake 3.20, build scripts
Updates the version and remove logic to find a CMake in 3rdParty.
* Removing backup path to ninja path in the build_ninja_windows.cmd
The backup path for finding ninja was coming from the Perforce depot which isn't available for o3de builds.
* Removing reference to 3rdParty Android SDK 29 from the build and run unit test script
The Android SDK is not part of the new 3rdParty system and users are expected to install the Android SDK on their own in order to build the engine for Android.
* Update the get_python scripts and README
No longer try to append a CMake path to LY_3RDPARTY_PATH, but do still
support LY_CMAKE_PATH because there are still uses of it. Remove
mention of an LY_3RDPARTY_PATH-relative CMake path from the README.md.
* Removing LY_NINJA_PATH from the build_ninja_windows.cmd
Co-authored-by: lumberyard-employee-dm <56135373+lumberyard-employee-dm@users.noreply.github.com>
Eric Phister
alexpete