Java UTs: Replace LogTester with slf4j

[pavel-mikula-sonarsource]

As per sonar-plugin-api 9.15 change log:
https://github.com/SonarSource/sonar-plugin-api/blob/master/CHANGELOG.md#915

We need to remove usages of LogTester

This is a prerequisite for #7595

[pavel-mikula-sonarsource]

Example of sonar-java PR: SonarSource/sonar-java#4416

They migrated:

Package	From	To
sonar-plugin-api	9.13.0.360	10.0.0.695
sonar-plugin-api-impl	9.5.0.56709	9.9.1.69595
sonar-testing-harness	9.5.0.56709	9.9.1.69595

Forced breaking changes:

• LogTesterJUnit5 has been moved:
  • The package has changed from org.sonar.api.utils.log to org.sonar.api.testfixtures.log
  • The LogTesterJUnit5 class is now in a new artifact that we have added sonar-plugin-api-test-fixtures 10.0.0.695
• Replace usage of org.sonar.api.utils.log.LoggerLevel with matching elements of org.slf4j.event.Level.
• Now LogTester only collects INFO by default, we use new LogTesterJUnit5().setLevel(Level.DEBUG) to also collect DEBUG
• org.sonar.api.SonarPlugin has been removed, we now use org.sonar.api.Plugin.
• We have to implement the new InputFile#md5Hash() method
• Rule repository name changes from SonarQube to Sonar

Deprecation changes:

• Replace thousands of calls to org.sonar.api.utils.log.Logger#get with org.slf4j.LoggerFactory.getLogger from a new provided dependency org.slf4j:slf4j-api:1.7.30

[mary-georgiou-sonarsource]

this has been already done in #7777
thanks @costin-zaharia-sonarsource!