classlib: add String.strip

classlib/src/main/java/org/teavm/classlib/java/lang/TString.java

@@ -475,6 +475,18 @@ public class TString extends TObject implements TSerializable, TComparable<TStri
         return substring(lower, upper + 1);
     }
 
+    public TString strip() {
+        var lower = 0;
+        var upper = length() - 1;
+        while (lower <= upper && Character.isWhitespace(charAt(lower))) {
+            ++lower;
+        }
+        while (lower <= upper && Character.isWhitespace(charAt(upper))) {
+            --upper;
+        }
+        return substring(lower, upper + 1);
+    }
+
     @Override
     public String toString() {
         return (String) (Object) this;

tests/src/test/java/org/teavm/classlib/java/lang/StringTest.java

@@ -201,6 +201,14 @@ public class StringTest {
         assertEquals("", "  ".trim());
     }
 
+    @Test
+    public void stripWorks() {
+        assertEquals("ab", "  ab   ".strip());
+        assertEquals("ab", "ab".strip());
+        assertEquals("", "  \t".strip());
+        assertEquals("ab", "\t\n \u2008ab\r\f".strip());
+    }
+
     @Test
     public void convertedToCharArray() {
         char[] array = "123".toCharArray();