Support concurrent access on ContextTypeRegistry.fContextTypes

This change adjusts ContextTypeRegistry to use a ConcurrentHashMap.

NOTE: As a result, iteration order of contextTypes() is no longer deterministic,
previously this was guaranteed by the underlying LinkedHashMap.

Fixes: #4020

Author: trancexpress

bundles/org.eclipse.text/src/org/eclipse/text/templates/ContextTypeRegistry.java

@@ -14,8 +14,8 @@
 package org.eclipse.text.templates;
 
 import java.util.Iterator;
-import java.util.LinkedHashMap;
 import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
 
 import org.eclipse.jface.text.templates.TemplateContextType;
 
@@ -32,7 +32,7 @@
 public class ContextTypeRegistry {
 
 	/** all known context types */
-	private final Map<String, TemplateContextType> fContextTypes= new LinkedHashMap<>();
+	private final Map<String, TemplateContextType> fContextTypes= new ConcurrentHashMap<>();
 
 	/**
 	 * Adds a context type to the registry. If there already is a context type