python3: Fix python3-pyvenv run-time dependency

Pyvenv is just a small script that uses venv to create virtual
environments.
https://www.python.org/dev/peps/pep-0405/#creating-virtual-environments

This patch adds the python3-venv module as a self-contained package which
python3-pyvenv must depend on at run-time.

The patch also provides the package python3-pyvenv from the pyhton3-venv
package.This is good for future-proofing since python3-pyvenv has been
deprecated and only python3-venv is now available in Python 3.6.
https://docs.python.org/3/library/venv.html.

Without this patch python3-pyvenv is broken because it is missing the
venv module at run-time. This patch specifies the newly created
python3-venv as a run-time dependency of python3-pyvenv.

(From OE-Core rev: effa141bfce55aab25142ee578c95383c755ad73)

Signed-off-by: Hugues Kamba <hugues.kamba@arm.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/recipes-devtools/python/python3/python3-manifest.json

@@ -1107,6 +1107,22 @@
             "${libdir}/python${PYTHON_MAJMIN}/__pycache__/getpass.*.pyc"
         ]
     },
+    "venv": {
+        "summary": "Provides support for creating lightweight virtual environments with their own site directories, optionally isolated from system site directories.",
+        "rdepends": [
+            "compression",
+            "core",
+            "logging",
+            "shell",
+            "stringold",
+            "unixadmin"
+        ],
+        "files": [
+            "${libdir}/python${PYTHON_MAJMIN}/venv",
+            "${bindir}/pyvenv*"
+        ],
+        "cached": []
+    },
     "xml": {
         "summary": "Python basic XML support",
         "rdepends": [