[18] False javadoc warning when using snippets and validate Missing Tag: "Description expected after @snippet"

If javadoc validation is turned on and a `@snippet` tag is used with the below setting JDT will give a warning.


```
Description expected after @snippet
```

Here are the javadoc prefs:

```
org.eclipse.jdt.core.compiler.problem.invalidJavadoc=warning
org.eclipse.jdt.core.compiler.problem.invalidJavadocTags=enabled
org.eclipse.jdt.core.compiler.problem.invalidJavadocTagsDeprecatedRef=disabled
org.eclipse.jdt.core.compiler.problem.invalidJavadocTagsNotVisibleRef=enabled
org.eclipse.jdt.core.compiler.problem.invalidJavadocTagsVisibility=public
org.eclipse.jdt.core.compiler.problem.missingJavadocComments=warning
org.eclipse.jdt.core.compiler.problem.missingJavadocCommentsOverriding=disabled
org.eclipse.jdt.core.compiler.problem.missingJavadocCommentsVisibility=public
org.eclipse.jdt.core.compiler.problem.missingJavadocTagDescription=all_standard_tags
org.eclipse.jdt.core.compiler.problem.missingJavadocTags=warning
org.eclipse.jdt.core.compiler.problem.missingJavadocTagsMethodTypeParameters=enabled
org.eclipse.jdt.core.compiler.problem.missingJavadocTagsOverriding=disabled
org.eclipse.jdt.core.compiler.problem.missingJavadocTagsVisibility=public
```

The below is the problematic setting.
```
org.eclipse.jdt.core.compiler.problem.missingJavadocTagDescription=all_standard_tags
```

Start by reproducing the warning with JDT javadoc validation enabled, the shown preferences, and a Javadoc @snippet tag. Trace the missing-tag-description validation for @snippet; done means the valid snippet no longer produces “Description expected after @snippet” while other applicable missing descriptions still do.

Written by the indexing model from the issue text.