Update dependencies for phpdocumentor/reflection

[kkmuffme]

"phpdocumentor/reflection" : "~3.0",

but latest version is https://github.com/phpDocumentor/Reflection 5.1.0

Due to this, this package cannot be used anymore in most installs, as there are dependency conflicts.

[iandunn]

There's also a conflict with wp-cli-psysh, and the wp-cli 2.7.0-alpha source version. wp-cli 2.6.0 binary works fine though.

[iandunn]

Related #211

[dmsnell]

In #251 I have proposed a different approach. phpDocumentor/Reflection is stuck in its latest version due to the overhaul of its _Reflector interfaces, but the existing phpdoc-parser code work with version ~3 with an updated nikic/php-parser.

The backwards-compatible breakages in nikic/php-parser are not difficult to account for until version ~4 of that library, so in phpDocumentor/Reflection#721 I have proposed an update to nikic/php-parser to version 3. The version numbers are confusing between the repos since there are multiple “version 3”s in play.

This means that with only a minimal change to the project we can restore the ability to parse WordPress code, relieving the pressure to make broader changes. This means that it will be easier for us to compare broad overhauls against the old docs, since something will be running against which to compare.