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
)
            );
        }
        Location location = userRegexNode.getLocation();
        int regexFlags = 0;
        for (int i = 0; i < flags.length(); ++i) {
            char flag = flags.charAt(i);
            regexFlags |= switch (flag) {
                case 'c' -> Pattern.CANON_EQ;
                case 'i' -> Pattern.CASE_INSENSITIVE;
                case 'l' -> Pattern.LITERAL;
                case 'm' -> Pattern.MULTILINE;
                case 's' -> Pattern.DOTALL;
                case 'U' -> Pattern.UNICODE_CHARACTER_CLASS;
                case 'u' -> Pattern.UNICODE_CASE;
                case 'x' -> Pattern.COMMENTS;
                default -> throw new IllegalArgumentException("invalid regular expression: unknown flag [" + flag + "]");
            };
        }
        Pattern compiled;
        try {
            compiled = Pattern.compile(pattern, regexFlags);
        } catch (PatternSyntaxException pse) {
            throw new Location(location.getSourceName(), location.getOffset() + 1 + pse.getIndex()).createError(
                new IllegalArgumentException(
                    "invalid regular expression: "
                        + "could not compile regex constant ["
                        + pattern
                        + "] with flags ["
                        + flags