Enable tracking for dynamically defined TypeVar instances

[ogrisel]

Ensure that dynamic typevars are tracked and reconciled as dynamic classes and enums for consistency of physical equality semantics in cloudpickle.

Follow-up on #350 by @valtron, also discussed in #351.

[codecov]

Codecov Report

Merging #353 into master will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@ Coverage Diff @@## master #353 +/- ##
=======================================
Coverage 93.32% 93.33% =======================================
Files 2 2 Lines 764 765 +1 Branches 156 156 =======================================
+ Hits 713 714 +1 
Misses 26 26 Partials 25 25 

Impacted Files	Coverage Δ
cloudpickle/cloudpickle_fast.py	95.72% <ø> (ø)
cloudpickle/cloudpickle.py	92.27% <100.00%> (+0.01%)	⬆️

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[ogrisel]

I checked that the new test did not pass prior to making the change.

[ogrisel]

I also include a renaming of _ensure_tracking to _get_or_create_tracker_id to make the code easier to follow by being more explicit about what this function returns.

[ogrisel]

@pierreglaser what do you think of making a release of cloudpickle to ship type annotation support?

[pierreglaser]

Sure, this deserves a minor relase on its own. We'll include #357 in the next bugfix release?

[ogrisel]

We'll include #357 in the next bugfix release?

+1 for dealing with the #357 in another release no to delay the shipping of the new type annotation support.