VirtualPythonEnv generator added

This generator can be used from the commandline as:
`conan install . -g VirtualPythonEnv`

It will then create a virtual environment in the build folder based on
the sys interpreter of a specified interpreter in the conanfile

The venv can be activated as normal
Contributes to CURA-9177_Fix_CI_CD

generators/VirtualPythonEnv.py

@@ -0,0 +1,82 @@
+import sys
+
+import os
+from io import StringIO
+
+from pathlib import Path
+
+from jinja2 import Template
+
+from conan.tools.env import VirtualRunEnv
+from conans.model import Generator
+
+
+class VirtualPythonEnv(Generator):
+
+    @property
+    def _venv_path(self):
+        if self.settings.os == "Windows":
+            return "Scripts"
+        return "bin"
+
+    @property
+    def filename(self):
+        filepath = str(Path(self.conanfile.generators_folder).joinpath("activate"))
+        if self.conanfile.settings.get_safe("os") == "Windows":
+            if self.conanfile.conf.get("tools.env.virtualenv:powershell", check_type = bool):
+                filepath += ".ps1"
+            else:
+                filepath += ".bat"
+        return filepath
+
+    @property
+    def content(self):
+        if hasattr(self.conanfile, "_python_interpreter"):
+            python_interpreter = self.conanfile._python_interpreter
+        else:
+            python_interpreter = sys.executable
+
+        self.conanfile.run(f"{python_interpreter} -m venv {self.conanfile.build_folder}", env = "conanrun")
+        python_interpreter = os.path.join(self.conanfile.build_folder, self._venv_path, "python")
+
+        buffer = StringIO()
+        self.conanfile.run(f"""{python_interpreter} -c 'import sysconfig; print(sysconfig.get_path("purelib"))'""", env = "conanrun",
+                           output = buffer)
+        pythonpath = buffer.getvalue().splitlines()[-1]
+
+        run_env = VirtualRunEnv(self.conanfile)
+        env = run_env.environment()
+
+        env.define_path("VIRTUAL_ENV", self.conanfile.build_folder)
+        env.prepend_path("PATH", os.path.join(self.conanfile.build_folder, self._venv_path))
+        env.prepend_path("PYTHONPATH", pythonpath)
+        env.unset("PYTHONHOME")
+        env.define("PS1", f"({self.conanfile.name}) ${{PS1:-}}")
+
+        envvars = env.vars(self.conanfile, scope = "run")
+
+        if hasattr(self.conanfile, "requirements_txts"):
+            if self.conanfile.requirements_txts:
+                if hasattr(self.conanfile.requirements_txts, "__iter__") and not isinstance(self.conanfile.requirements_txts, str):
+                    for req_txt in self.conanfile.requirements_txts:
+                        with envvars.apply():
+                            self.conanfile.run(
+                                f"{python_interpreter} -m pip install -r {os.path.join(self.conanfile.source_folder, req_txt)}",
+                                run_environment = True, env = "conanrun")
+                else:
+                    with envvars.apply():
+                        self.conanfile.run(
+                            f"{python_interpreter} -m pip install -r {os.path.join(self.conanfile.source_folder, self.conanfile.requirements_txts)}",
+                            run_environment = True, env = "conanrun")
+
+        template = Template("""\
+deactivate()
+{
+{% for k, v in envvars.items() %}export {{ k }}=$OLD_{{ k }}
+unset OLD_{{ k }}
+{% endfor %}}
+
+{% for k, v in envvars.items() %}export OLD_{{ k }}=${{ k }}
+export {{ k }}={{ v }}
+{% endfor %}""")
+        return template.render(envvars = envvars)