IDEA-328157 Allow gradle installations to be read-only

[JFronny]

Currently, the Gradle tool window permits any directory containing the correct content to be configured as the Gradle installation home:

intellij-community/plugins/gradle/src/org/jetbrains/plugins/gradle/service/settings/IdeaGradleProjectSettingsControlBuilder.java

Lines 419 to 421 in 0e71313

	if (GradleInstallationManager.getInstance().isGradleSdkHome(project, Path.of(myGradleHomePathField.getText()))) {
	myGradleHomeSettingType = GradleLocationSettingType.EXPLICIT_CORRECT;
	}

The new project wizard and settings component on the other hand use CHECK_DIRECTORY in addition, which also checks whether the directory is writable, even though this is never needed here:

intellij-community/platform/platform-impl/src/com/intellij/openapi/ui/validation/validations.kt

Lines 39 to 46 in 0e71313

	val CHECK_DIRECTORY: DialogValidation.WithParameter<() -> String> = validationPathErrorFor { path ->
	when {
	!path.exists() -> null
	!path.isWritable() -> UIBundle.message("label.project.wizard.new.project.directory.not.writable.error", path.name)
	!path.isDirectory() -> UIBundle.message("label.project.wizard.new.project.file.not.directory.error", path.name)
	else -> null
	}
	}

As a consequence, users that use a package manager first have to create their projects with gradlew, then manually delete the gradlew files and change the installation home in the tool window instead of just creating their project.

This PR fixes this by providing a variant of CHECK_DIRECTORY that does not check for writeability.