Update checkstyle to 10.0 and fix various related issues

[Stypox]

What is it?

• Bugfix (user facing)
• Feature (user facing)
• Codebase improvement (dev facing)
• Meta improvement to the project (dev facing)

Description of the changes in your PR

• Update checkstyle from 9.3 to 10.0 (changelog).
• Put checkstyle files into checkstyle/ subfolder so that the gradle task does not implicitly depend on the whole project, fixing many warnings during build and possibly increasing build performance.
  • The warnings were like this: Execution optimizations have been disabled for task ':app:runCheckstyle' to ensure correctness due to the following reasons: Gradle detected a problem with the following location: 'XXX/NewPipe'. Reason: Task ':app:runCheckstyle' uses this output of task ':app:XXX' without declaring an explicit or implicit dependency. This can lead to incorrect results being produced, depending on what order the tasks are executed. Please refer to https://docs.gradle.org/7.4/userguide/validation_problems.html#implicit_dependency for more details about this problem.
• Remove unused SuppressionXpathFilter from config file.
• Remove outdated suppressions from suppressions file.

Spoiler alert

I'm adding checkstyle to NewPipeExtractor ;-)

Due diligence

• I read the contribution guidelines.

[litetex]

LGTM

[Stypox]

I pushed a commit that replaces some suppressions in the suppressions file with @SuppressWarnings, so that the suppression is written right where it acts. I also added @SuppressWarnings to the four [WARN] that have been haunting us for years, so now there is no misleading red output anymore in the build process ;-)

[sonarqubecloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

No Coverage information
0.0% Duplication

[triallax]

I pushed a commit that replaces some suppressions in the suppressions file with @SuppressWarnings, so that the suppression is written right where it acts.

You know, I've always found it weird that we had checkstyle suppressions in a separate file; what if they become outdated or something? This is perfect and easier to follow.