android-ndk: set CONAN_CMAKE_SYSTEM_PROCESSOR

[madebr]

Specify library name and version: lib/1.0

When cross building to armv8 android, we need to set CMAKE_SYSTEM_PROCESSOR=aarch64 explicitly.

These are the available values

Without this pr, this error is shown

(This is where I encountered it)

Also,

• I've reformatted the recipe to use double quotes + f-strings
• encoded the valid os/arch in conandata.yml. If the recipe cannot find sources in the conandata.yml, then it's not supported
• Also moved the download from source to build. android-ndk is a package of a binary artifact, and is different for each os/arch.

---

• I've read the guidelines for contributing.
• I've followed the PEP8 style guides for Python code in the recipes.
• I've used the latest Conan client version.
• I've tried at least one configuration locally with the
  conan-center hook activated.

[conan-center-bot]

All green in build 4 (8906cccf6951d242ecb4099f6a6696ff12f22de9):

• android-ndk/r23@:
  All packages built successfully! (All logs)

• android-ndk/r22b@:
  All packages built successfully! (All logs)

• android-ndk/r22@:
  All packages built successfully! (All logs)

• android-ndk/r21e@:
  All packages built successfully! (All logs)

• android-ndk/r21d@:
  All packages built successfully! (All logs)

[uilianries]

LGTM