BUG : fix for text path rendering issues

[tacaswell]

Suggested by @leejjoon.

Fixes #2889

[tacaswell]

This still needs a test + docs.

[pelson]

This still needs a test + docs.

I'm not sure about the docs, but the test should be relatively straight forward. It also appears to be impacting other test results, suggesting that this functionality is fixing already tested behaviour.

I'm 👍 on merging the method once the (potentially simple, picture-less) test exists.

[tacaswell]

It looks like it is breaking existing behavior....

I don't really understand what is going on here well enough to write tests.

[pelson]

`FAIL: matplotlib.tests.test_patheffects.test_patheffect3``

This is good. It fixes an image which I added a few months ago (in which I struggled to get the font to be the expected size!!!).

FAIL: matplotlib.tests.test_patheffects.test_collection

This is good too - it fills the space in the boxes that I (again) struggled to understand why it didn't in the first place (test also added by me a few months ago).

So all in all - this is doing the right thing 😄

[pelson]

Closed in favour of #3081.