Implement processing of conditions

[nforro]

This is not a full support for conditions, i.e. it doesn't re-solve #231 where an entire section can be conditionalized (however, the new process_conditions() function is generic enough to be used as a base for the resolution of that issue), nevertheless I think it's quite an improvement.

Note that macro definitions have to be parsed twice, because a macro definition can contain a condition (see https://src.fedoraproject.org/rpms/kernel/blob/rawhide/f/kernel.spec for examples), and vice versa, a condition can encapsulate a macro definition.

Macro definitions and tags gained a valid attribute that can be used to determine if that particular macro definition/tag is valid and can affect other entities in the spec file or if it would be ignored when parsing the spec file with RPM. This will be used to fix Specfile.update_value() and Specfile.update_tag(), but it could be beneficial for other use cases as well.

Related to packit/packit#2033.

RELEASE NOTES BEGIN

Macro definitions and tags gained a new valid attribute. A macro definition/tag is considered valid if it doesn't appear in a false branch of any condition appearing in the spec file.

RELEASE NOTES END

[lachmanfrantisek]

Note that macro definitions have to be parsed twice

Are there any performance concerns? (E.g. in Copr)

[nforro]

Are there any performance concerns? (E.g. in Copr)

Well, it will make things slower, but it shouldn't be noticeable. Parsing texlive.spec takes roughly 100ms more (that's 100ms out of 9.5 seconds).

[lachmanfrantisek]

Just wow, this really shows what it means to parse the specfile..;-D

I am only not sure if I am able to review this..;) So, just a few code-style nit picks.

[nforro]

recheck

[softwarefactory-project-zuul]

Build succeeded.
https://softwarefactory-project.io/zuul/t/packit-service/buildset/114fea4049074c34b0de7b5c61975e0b

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✔️ specfile-tests-pip-deps SUCCESS in 1m 00s

[softwarefactory-project-zuul]

Build succeeded (gate pipeline).
https://softwarefactory-project.io/zuul/t/packit-service/buildset/6b516068e2e14fcc99fc5595fd9453ca

✔️ pre-commit SUCCESS in 1m 22s