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/controls.cpp

@@ -549,8 +549,7 @@ const ControlValue &ControlList::get(unsigned int id) const
 	const auto ctrl = idmap_->find(id);
 	if (ctrl == idmap_->end()) {
 		LOG(Controls, Error)
-			<< std::hex << std::setfill('0')
-			<< "Control 0x" << std::setw(8) << id
+			<< "Control " << utils::hex(id)
 			<< " is not supported";
 		return zero;
 	}
@@ -579,8 +578,7 @@ void ControlList::set(unsigned int id, const ControlValue &value)
 	const auto ctrl = idmap_->find(id);
 	if (ctrl == idmap_->end()) {
 		LOG(Controls, Error)
-			<< std::hex << std::setfill('0')
-			<< "Control 0x" << std::setw(8) << id
+			<< "Control 0x" << utils::hex(id)
 			<< " is not supported";
 		return;
 	}