Ignore suppressions for no-unused-imports rule

[paul-dingemans]

Description

Ignore suppressions for no-unused-imports rule

Imports which are only used in code blocks which are suppressed for ktlint should not be reported as unused as removal results in compilation errors.

Refactored the code so that a rule can be marked with interface IgnoreKtlintSuppressions to indicate that all suppressions for this rule are to be ignored.

Closes #2696

Checklist

Before submitting the PR, please check following (checks which are not relevant may be ignored):

• Commit message are well written. In addition to a short title, the commit message also explain why a change is made.
• At least one commit message contains a reference Closes #<xxx> or Fixes #<xxx> (replace<xxx> with issue number)
• Tests are added
• KtLint format has been applied on source code itself and violations are fixed
• PR title is short and clear (it is used as description in the release changelog)
• PR description added (background information)

Documentation is updated. See difference between snapshot and release documentation

• Snapshot documentation in case documentation is to be released together with a code change
• Release documentation in case documentation is related to a released version of ktlint and has to be published as soon as the change is merged to master