Collect WHEEL files for installed python wheels

[pombredanne]

A WHEEL file has the Tag needed to reconstruct the file_name of the wheel to construct a proper detailed PURL:

Wheel-Version: 1.0
Generator: bdist_wheel (0.35.1)
Root-Is-Purelib: false
Tag: cp27-cp27m-win_amd64

See also

scancode-toolkit/etc/scripts/utils_thirdparty.py

Line 1148 in 4b57a7f

Represents a wheel file.

where we have the code to reconstruct wheel file_name from tag

[kaokab33]

I've submitted a PR to address this issue: #4776

The PR parses .dist-info/WHEEL files to extract wheel tags and stores them in extra_data, which can be used to reconstruct the original wheel filename for building detailed PURLs.

Would appreciate any feedback. Thanks!