Add explicit casts to deficient numeric types

To avoid `possible lossy conversion from int to byte/short` errors when
using `AnnotationValue`s for `byte` or `short` in some contexts, e.g.:

```
  void f() {
    g(0);
  }

  void g(byte b) {}
```

```
error: incompatible types: possible lossy conversion from int to byte
    g(0);
      ^
```
RELNOTES=n/a
PiperOrigin-RevId: 386478953

common/src/main/java/com/google/auto/common/AnnotationOutput.java

@@ -74,6 +74,18 @@ private String formatType(TypeMirror typeMirror) {
       return null;
     }
 
+    @Override
+    public @Nullable Void visitByte(byte b, StringBuilder sb) {
+      sb.append("(byte) ").append(b);
+      return null;
+    }
+
+    @Override
+    public @Nullable Void visitShort(short s, StringBuilder sb) {
+      sb.append("(short) ").append(s);
+      return null;
+    }
+
     @Override
     public @Nullable Void visitChar(char c, StringBuilder sb) {
       appendQuoted(sb, c);

common/src/test/java/com/google/auto/common/AnnotationValuesTest.java

@@ -376,10 +376,10 @@ public void toSourceString() {
             .put("intValues", "{1, 2}")
             .put("longValue", "6L")
             .put("longValues", "{3L, 4L}")
-            .put("byteValue", "7")
-            .put("byteValues", "{8, 9}")
-            .put("shortValue", "10")
-            .put("shortValues", "{11, 12}")
+            .put("byteValue", "(byte) 7")
+            .put("byteValues", "{(byte) 8, (byte) 9}")
+            .put("shortValue", "(short) 10")
+            .put("shortValues", "{(short) 11, (short) 12}")
             .put("floatValue", "13.0F")
             .put("floatValues", "{14.0F, 15.0F}")
             .put("doubleValue", "16.0")