If a hex literal has an 'd' of 'f' in it, such as '0xf' or '0xd', the compiler fails with illegal tree structure.

The other hex literals work.  The issue is probably related to using `f` and `d` in float and double literals.

```
    public void testHexCollisionDouble() {
        assertEquals(13, exec("return 0xd"));
    }

    public void testHexCollisionFloat() {
        assertEquals(15, exec("return 0xf"));
    }

    public void testHex() throws Exception {
        for (int i = 0; i <= 15; i++) {
            String hex = Integer.toHexString(i);
            if ("d".equals(hex) || "f".equals(hex)) {
                continue;
            }
            assertEquals(i, exec("return 0x" + hex));
            assertEquals(i, exec("return 0x" + hex.toUpperCase(Locale.ROOT)));
            assertEquals(i, exec("return 0X" + hex));
            assertEquals(i, exec("return 0X" + hex.toUpperCase(Locale.ROOT)));
        }
    }
```
modules/lang-painless/src/main/java/org/elasticsearch/painless/phase/DefaultSemanticAnalysisPhase.java
if (getter != null
                && (getter.returnType() == void.class
                    || getter.typeParameters().size() != 1
                    || getter.typeParameters().get(0) != int.class)) {
                throw userBraceNode.createError(
                    new IllegalArgumentException("Illegal list get shortcut for type [" + canonicalClassName + "].")
                );
            }
            if (setter != null && (setter.typeParameters().size() != 2 || setter.typeParameters().get(0) != int.class)) {
                throw userBraceNode.createError(
                    new IllegalArgumentException("Illegal list set shortcut for type [" + canonicalClassName + "].")
                );
            }
            if (getter != null
                && setter != null
                && (getter.typeParameters().get(0).equals(setter.typeParameters().get(0)) == false
                    || getter.returnType().equals(setter.typeParameters().get(1)) == false)) {
                throw userBraceNode.createError(new IllegalArgumentException("Shortcut argument types must match."));
            }
            if ((read == false || getter != null) && (write == false || setter != null)) {
                semanticScope.setCondition(userIndexNode, Read.class);
                semanticScope.putDecoration(userIndexNode, new TargetType(int.class));
                checkedVisit(userIndexNode, semanticScope);
                decorateWithCast(userIndexNode, semanticScope);
                valueType = setter != null ? setter.typeParameters().get(1) : getter.returnType();
                if (getter != null) {
                    semanticScope.putDecoration(userBraceNode, new GetterPainlessMethod(getter));
                }
                if (setter != null) {
                    semanticScope.putDecoration(userBraceNode, new SetterPainlessMethod(setter));