[INTERNAL] JSDoc: Add check for copyright notice

Checks for a copyright notice at the beginning of each file.
The comment doesn't need to be the first comment but it must be placed
before any code starts.

This implements the same check as the internal validation rule
DOCUMENTATION__COPYRIGHT_NOTICE_MISSING.

JIRA: CPOUI5FOUNDATION-329

Cherry picked from SAP/openui5@bcb5110

lib/processors/jsdoc/lib/ui5/plugin.js

@@ -2652,6 +2652,27 @@ exports.astNodeVisitor = {
 				processPotentialEnum(node.expression.right, comment);
 			}
 
+		} else if ( node.type === Syntax.File ) {
+			// Check for copyright notice
+
+			let programBodyStart;
+			if ( node.program.body.length >= 1 ) {
+				programBodyStart = node.program.body[0].start
+			} else {
+				// File has no code at all
+				programBodyStart = Infinity;
+			}
+
+			const hasCopyrightComment = ( node.comments || [] ).some(function(commentBlock) {
+				return (
+					// Copyright comments must be at the top of the file, not between some code or at the end
+					commentBlock.end <= programBodyStart &&
+					/copyright|\(c\)|released under|license|\u00a9/.test(commentBlock.value)
+				);
+			});
+			if ( !hasCopyrightComment ) {
+				error(`document doesn't contain a copyright notice: ${currentSourceName}`);
+			}
 		}
 	}