fix(pdfccittfaxdecoder): Remove whitespace in _bitlength operator

This fixes a compilation warning with newer clang version.
Indeed, the whitespace between "" and _bitlength is no longer
allowed. This was permitted in older versions of the standard but has
since been deprecated.

```
error: identifier '_bitlength' preceded by whitespace in a literal
operator declaration is deprecated
[-Werror,-Wdeprecated-literal-operator]
     27 | constexpr uint8_t operator "" _bitlength()
        |                   ~~~~~~~~~~~~^~~~~~~~~~
        |                   operator""_bitlength
```

Pdf4QtLibCore/sources/pdfccittfaxdecoder.cpp

@@ -28,7 +28,7 @@ namespace pdf
 {
 
 template<char... Digits>
-constexpr uint8_t operator "" _bitlength()
+constexpr uint8_t operator ""_bitlength()
 {
     return sizeof...(Digits);
 }