Added support for Apache Validate (#769)

Added support for Apache Validate:
https://github.com/apache/commons-lang/blob/master/src/main/java/org/apache/commons/lang3/Validate.java

We recently started to use these Apache methods to validate some data
but quickly found out that NullAway doesn't support them since they are
not properly annotated. Here's a fix that adds support for these methods
along with test cases for each method.

I noticed that Apache library generally has different validation methods
for String, Map and Collection, but they all end up with the same
signature when analyzed by NullAway (probably because these methods use
generics).
Examples of such methods:
```java
public static <T extends Collection<?>> T notEmpty(final T collection) {
}

public static <T extends Map<?, ?>> T notEmpty(final T map) {
}

public static <T extends CharSequence> T notEmpty(final T chars) {
}
```

But I decided to add a separate unit test for each of these methods in
case NullAway will change how it generates method's signature in the
future.

nullaway/src/main/java/com/uber/nullaway/handlers/LibraryModelsHandler.java

@@ -452,6 +452,54 @@ private static class DefaultLibraryModels implements LibraryModels {
                     "org.junit.jupiter.api.Assertions",
                     "assertNotNull(java.lang.Object,java.util.function.Supplier<java.lang.String>)"),
                 0)
+            .put(methodRef("org.apache.commons.lang3.Validate", "<T>notNull(T)"), 0)
+            .put(
+                methodRef(
+                    "org.apache.commons.lang3.Validate",
+                    "<T>notNull(T,java.lang.String,java.lang.Object...)"),
+                0)
+            .put(
+                methodRef(
+                    "org.apache.commons.lang3.Validate",
+                    "<T>notEmpty(T[],java.lang.String,java.lang.Object...)"),
+                0)
+            .put(methodRef("org.apache.commons.lang3.Validate", "<T>notEmpty(T[])"), 0)
+            .put(
+                methodRef(
+                    "org.apache.commons.lang3.Validate",
+                    "<T>notEmpty(T,java.lang.String,java.lang.Object...)"),
+                0)
+            .put(methodRef("org.apache.commons.lang3.Validate", "<T>notEmpty(T)"), 0)
+            .put(
+                methodRef(
+                    "org.apache.commons.lang3.Validate",
+                    "<T>notBlank(T,java.lang.String,java.lang.Object...)"),
+                0)
+            .put(methodRef("org.apache.commons.lang3.Validate", "<T>notBlank(T)"), 0)
+            .put(
+                methodRef(
+                    "org.apache.commons.lang3.Validate",
+                    "<T>noNullElements(T[],java.lang.String,java.lang.Object...)"),
+                0)
+            .put(methodRef("org.apache.commons.lang3.Validate", "<T>noNullElements(T[])"), 0)
+            .put(
+                methodRef(
+                    "org.apache.commons.lang3.Validate",
+                    "<T>noNullElements(T,java.lang.String,java.lang.Object...)"),
+                0)
+            .put(methodRef("org.apache.commons.lang3.Validate", "<T>noNullElements(T)"), 0)
+            .put(
+                methodRef(
+                    "org.apache.commons.lang3.Validate",
+                    "<T>validIndex(T[],int,java.lang.String,java.lang.Object...)"),
+                0)
+            .put(methodRef("org.apache.commons.lang3.Validate", "<T>validIndex(T[],int)"), 0)
+            .put(
+                methodRef(
+                    "org.apache.commons.lang3.Validate",
+                    "<T>validIndex(T,int,java.lang.String,java.lang.Object...)"),
+                0)
+            .put(methodRef("org.apache.commons.lang3.Validate", "<T>validIndex(T,int)"), 0)
             .build();
 
     private static final ImmutableSetMultimap<MethodRef, Integer> EXPLICITLY_NULLABLE_PARAMETERS =