Add the upper and lower format modifier functions.

Add a generic mechanism to easily create new simple format modifiers,
and use it to two new format modifiers to transform the substituted text
into lower case or upper case.

Author: gouttegd

ext/src/main/java/org/incenp/obofoundry/sssom/transform/MappingFormatter.java

@@ -234,6 +234,8 @@ public void setStandardModifiers() {
         setModifier(new SSSOMTFlattenFunction());
         setModifier(new SSSOMTDefaultModifierFunction());
         setModifier(new SSSOMTReplaceModifierFunction());
+        setModifier(new SimpleStringModifierFunction("upper", (s) -> s.toUpperCase()));
+        setModifier(new SimpleStringModifierFunction("lower", (s) -> s.toLowerCase()));
         if ( pfxMgr != null ) {
             setModifier(new SSSOMTShortFunction(pfxMgr));
             setModifier(new SSSOMTPrefixFunction(pfxMgr));

ext/src/main/java/org/incenp/obofoundry/sssom/transform/SimpleStringModifierFunction.java

@@ -0,0 +1,66 @@
+/*
+ * SSSOM-Java - SSSOM library for Java
+ * Copyright © 2025 Damien Goutte-Gattat
+ * 
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package org.incenp.obofoundry.sssom.transform;
+
+import java.util.List;
+import java.util.function.Function;
+
+/**
+ * Represents a simple format modifier function that does not take any argument.
+ * <p>
+ * This class is intended to allow creating simple modifiers without having to
+ * create a new dedicated class. For example, to create a modifier that turns
+ * its input into lowercase:
+ * 
+ * <pre>
+ * new SimpleStringModifierFunction("lower", (input) -&gt; input.toLowerCase());
+ * </pre>
+ */
+public class SimpleStringModifierFunction extends BaseStringModifierFunction {
+
+    private String name;
+    private Function<String, String> func;
+
+    /**
+     * Creates a new instance.
+     * 
+     * @param name The name of the modifier function to create.
+     * @param func The implementation of the function.
+     */
+    public SimpleStringModifierFunction(String name, Function<String, String> func) {
+        this.name = name;
+        this.func = func;
+    }
+
+    @Override
+    public String getName() {
+        return name;
+    }
+
+    @Override
+    public String getSignature() {
+        return "";
+    }
+
+    @Override
+    protected String apply(Object value, List<String> extra) {
+        return func.apply(value.toString());
+    }
+
+}

ext/src/site/apt/sssom-transform.apt

@@ -1034,6 +1034,11 @@ predicate==* -> replace("object_id", "https://meshb.nlm.nih.gov/record/ui[?]ui="
   shortened identifier to keep only the suffix (also known as the “local
   name”).
 
+*** 6.5.9. <lower> and <upper>
+
+  These modifiers turn the substituted text into lower case and upper
+  case, respectively.
+  
 * 7. Grouping rules
 
   If several actions need to be performed on the same selection of