tensorflow: cleanup and merge with libtensorflow

This merges work done by yorickvP and timokau in #63208 and #63616 respectively.
Now the derivation builds both libtensorflow and the Python package and puts them into
different outputs.

Quite a bit of improvements were done on the top, including:

* Use official tag revision as source, not a branch;
* Use all system libraries possible (before only one was actually used);
* Move various environment variables to the derivation itself from hooks;
* Use source Python build instead of wheel build to ensure fixup hooks do their important jobs on libraries;
* And more that I forgot!

pkgs/development/python-modules/tensorflow/system-jsoncpp.patch

@@ -0,0 +1,21 @@
+diff --git a/third_party/systemlibs/jsoncpp.BUILD b/third_party/systemlibs/jsoncpp.BUILD
+index 526fd0c418..646f3fdcea 100644
+--- a/third_party/systemlibs/jsoncpp.BUILD
++++ b/third_party/systemlibs/jsoncpp.BUILD
+@@ -7,6 +7,7 @@ filegroup(
+ 
+ HEADERS = [
+     "include/json/autolink.h",
++    "include/json/allocator.h",
+     "include/json/config.h",
+     "include/json/features.h",
+     "include/json/forwards.h",
+@@ -23,7 +24,7 @@ genrule(
+     cmd = """
+       for i in $(OUTS); do
+         i=$${i##*/}
+-        ln -sf $(INCLUDEDIR)/jsoncpp/json/$$i $(@D)/include/json/$$i
++        ln -sf $(INCLUDEDIR)/json/$$i $(@D)/include/json/$$i
+       done
+     """,
+ )