[EXPERIMENTAL] allow test_packages run in emulated environment

[perseoGI]

Changelog: Feature: Allow running test_package in an emulated environment
Docs: https://github.com/conan-io/docs/pull/XXXX

Directly related to #19940

This PR makes use of the "incubating" emulator key in order to allow running the test package in a cross compilation.
This could be used in Conan Center Index in order to compile and test new configurations (e.g. emscripten, android).

Examples

Create a basic CMake library:

$ conan new cmake_lib -d name="cmake_lib" -d version=1.0 -o cmake_lib

Android NDK

[settings]
arch=armv8
build_type=Release
compiler=clang
compiler.cppstd=17
compiler.libcxx=c++_static
compiler.version=19
os=Android
os.api_level=28
[tool_requires]
*: android-ndk/[*]

[conf]
tools.build:compiler_executables={'emulator': '{{profile_dir}}/android_emulator.sh'}

android_emulator.sh -> wrapper to call Android Studio emulator (this could be far simpler if we use qemu-user emulator from a Linux environment (Macos only supports qemu-system which does not allow direct invokation)

For this, we create a wrapper:

#!/bin/bash
set -e

BINARY="$1"
shift

BINARY_NAME="$(basename "$BINARY")"
REMOTE_PATH="/data/local/tmp/$BINARY_NAME"

echo "Pushing $BINARY to emulator at $REMOTE_PATH"
adb push "$BINARY" "$REMOTE_PATH" >/dev/null 2>&1
adb shell chmod +x "$REMOTE_PATH"

echo "Executing $REMOTE_PATH with arguments: $@"
OUTPUT=$(adb shell "$REMOTE_PATH" "$@" 2>&1; echo "EXIT_CODE:$?")
EXIT_CODE=$(echo "$OUTPUT" | grep -o 'EXIT_CODE:[0-9]*' | cut -d: -f2)
echo "$OUTPUT" | grep -v 'EXIT_CODE:'

adb shell rm -f "$REMOTE_PATH" >/dev/null 2>&1
exit ${EXIT_CODE:-1}

$ conan create -pr android
...

======== Testing the package: Executing test ========
cmake_lib/1.0 (test package): Running test()
cmake_lib/1.0 (test package): RUN: /Users/perseo/sources/test/meson/cmake_emulator/android_emulator.sh ./example
Pushing ./example to emulator at /data/local/tmp/example
Executing /data/local/tmp/example with arguments: 
cmake_lib/1.0: Hello World Release!
  cmake_lib/1.0: __aarch64__ defined
  cmake_lib/1.0: __cplusplus201703
  cmake_lib/1.0: __GNUC__4
  cmake_lib/1.0: __GNUC_MINOR__2
  cmake_lib/1.0: __clang_major__21
cmake_lib/1.0 test_package

The test_package will be passed to the emulator wrapper, which will push the binary to the emulator and run from it!

Emscripten/Node

An easier example will be to use emscripten toolchain to cross-compile to WASM and then, invoke node directly.

[settings]
arch=wasm
build_type=Release
compiler=emcc
compiler.cppstd=17
compiler.libcxx=libc++
compiler.version=5.0.3
os=Emscripten

[conf]
tools.build:compiler_executables={'c':'emcc', 'cpp':'em++', 'emulator': '/tmp/node_wrapper.sh --trace-exit'}

$ conan create -pr wasm
...
======== Testing the package: Executing test ========
cmake_lib/1.0 (test package): Running test()
cmake_lib/1.0 (test package): RUN: node ./example
[EMULATOR] node --trace-exit ./example
cmake_lib/1.0: Hello World Release!
  cmake_lib/1.0: __cplusplus201703
  cmake_lib/1.0: __GNUC__4
  cmake_lib/1.0: __GNUC_MINOR__2
  cmake_lib/1.0: __clang_major__23
cmake_lib/1.0 test_package