libcamera: value_node: Support looking up descendant node by path

Looking up a descendant node based on a path is a common operation. Add
a helper function to do so, to avoid loops in the callers.

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

include/libcamera/internal/value_node.h

@@ -237,6 +237,7 @@ public:
 	bool contains(std::string_view key) const;
 	ValueNode *at(std::string_view key);
 	const ValueNode &operator[](std::string_view key) const;
+	const ValueNode &operator[](std::initializer_list<std::string_view> path) const;
 
 	ValueNode *add(std::unique_ptr<ValueNode> &&child);
 	ValueNode *add(std::string key, std::unique_ptr<ValueNode> &&child);