internal/report: refactor - add Description type

Add named type Description for Report descriptions, and move logic
to lint descriptions to method Description.lint.

Change-Id: Ie198b7c9ec89fe3dc64676e033d8ebe12145b3ea

squash description

Change-Id: I92d376181f4472010024c3ffaf0ef597b7ad1ac0
Reviewed-on: https://go-review.googlesource.com/c/vulndb/+/542357
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Damien Neil <dneil@google.com>
diff --git a/internal/report/fix.go b/internal/report/fix.go
index 86de67c..18fe88f 100644
--- a/internal/report/fix.go
+++ b/internal/report/fix.go
@@ -27,7 +27,7 @@
 		*sp = fixLineLength(*sp, maxLineLength)
 	}
 	fixLines((*string)(&r.Summary))
-	fixLines(&r.Description)
+	fixLines((*string)(&r.Description))
 	if r.CVEMetadata != nil {
 		fixLines(&r.CVEMetadata.Description)
 	}