libcamera: utils: Add hex stream output helper

Add a utils::hex() function that simplifies writing hexadecimal values
to an ostream. The function handles the '0x' prefix, the field width and
the fill character automatically. Use it through the libcamera code
base, and add a test.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Niklas Söderlund <niklas.soderlund@ragnatech.se>
Reviewed-by: Jacopo Mondi <jacopo@jmondi.org>

src/libcamera/stream.cpp

@@ -16,6 +16,7 @@
 #include <libcamera/request.h>
 
 #include "log.h"
+#include "utils.h"
 
 /**
  * \file stream.h
@@ -367,11 +368,7 @@ StreamConfiguration::StreamConfiguration(const StreamFormats &formats)
 std::string StreamConfiguration::toString() const
 {
 	std::stringstream ss;
-
-	ss.fill(0);
-	ss << size.toString() << "-0x" << std::hex << std::setw(8)
-	   << pixelFormat;
-
+	ss << size.toString() << "-" << utils::hex(pixelFormat);
 	return ss.str();
 }