libcamera: yaml_parser: Un-friend YamlParserContext from YamlObject

YamlParserContext is a friend of the YamlObject class to access private
member variables. Now that YamlObject exposes functions to set a value
and add children, this is not needed anymore. Decouple the two classes.

The YamlParserContext::readValue() function now takes a const reference
to the EventPtr as the YamlParserContext::parseNextYamlObject() function
needs to access it in the error handler.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Isaac Scott <isaac.scott@ideasonboard.com>
Reviewed-by: Barnabás Pőcze <barnabas.pocze@ideasonboard.com>

include/libcamera/internal/yaml_parser.h

@@ -205,7 +205,6 @@ private:
 
 	template<typename T>
 	friend struct Accessor;
-	friend class YamlParserContext;
 
 	enum class Type {
 		Dictionary,