[BUG] Gradle plugin uses string type instead of file type

Description

The field inputSpec in the task ValidateTask does not use the correct type.

https://github.com/OpenAPITools/openapi-generator/blob/master/modules/openapi-generator-gradle-plugin/src/main/kotlin/org/openapitools/generator/gradle/plugin/tasks/ValidateTask.kt#L55-L57

The provided annotation for input/output checks won't work properly. @InputFile has been assigned but the type is not a file property type. Incremental build functionality and build caching work as expected. For example, if you change the contents of the assigned file provided as a string. The string doesn't change, however, the content does and therefore doesn't trigger a re-run of the task.

This issue isn't limited to the task ValidateTask. The same issue applies to other task types provided by the plugin.

openapi-generator version

OpenAPI Gradle plugin 7.1.0.

OpenAPI declaration file content or url

plugins {
    id "org.openapi.generator" version "7.1.0"
}

openApiValidate {
    inputSpec = "$rootDir/petstore-v3.0-invalid.yaml"
    recommend = true
}

Steps to reproduce

Run the task openApiValidate.

Suggest a fix

The field should use the type RegularFileProperty.

Start with modules/openapi-generator-gradle-plugin/src/main/kotlin/org/openapitools/generator/gradle/plugin/tasks/ValidateTask.kt at lines 55-57, then inspect the other task types provided by the plugin for similarly typed inputSpec fields. Run openApiValidate with the supplied configuration and change the contents of the referenced file; done means the relevant file-property inputs trigger the task again and are handled correctly by Gradle input/output checks.