Optimize constructor links

[tristanlatr]

Fix #786

[github-actions[bot]]

Diff from pydoctor_primer, showing the effect of this PR on open source code:

numpy (https://github.com/numpy/numpy): typechecking got 1.11x slower (187.6s -> 209.1s)
(Performance measurements are based on a single noisy sample)

[github-actions[bot]]

According to pydoctor_primer, this change doesn't affect pydoctor warnings on a corpus of open source code. ✅

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 88.57143% with 4 lines in your changes are missing coverage. Please review.

Project coverage is 92.60%. Comparing base (936db93) to head (7ec24e9).

Files	Patch %	Lines
pydoctor/epydoc2stan.py	88.23%	1 Missing and 1 partial :warning:
pydoctor/model.py	93.33%	0 Missing and 1 partial :warning:
pydoctor/templatewriter/pages/__init__.py	66.66%	0 Missing and 1 partial :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #787 +/- ## ========================================== - Coverage 92.64% 92.60% -0.04% ========================================== Files 47 47 Lines 8384 8389 +5 Branches 1848 1850 +2 ========================================== + Hits 7767 7769 +2 - Misses 355 356 +1 - Partials 262 264 +2 ```

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.

[github-actions[bot]]

According to pydoctor_primer, this change doesn't affect pydoctor warnings on a corpus of open source code. ✅

[github-actions[bot]]

According to pydoctor_primer, this change doesn't affect pydoctor warnings on a corpus of open source code. ✅