Add body.find_all() to Python bindings.

This enables to generate a list of all body children of a given type.

Also, add recursive option to mjs_firstChild and mjs_nextChild. Fixes #2112.

PiperOrigin-RevId: 681039348
Change-Id: Iebbb26fd5ec314150206edfdddd88633baa0bec6

doc/APIreference/functions.rst

@@ -4205,7 +4205,7 @@ mjs_firstChild
 
 .. mujoco-include:: mjs_firstChild
 
-Return body's first child of given type.
+Return body's first child of given type. If recurse is nonzero, also search the body's subtree.
 
 .. _mjs_nextChild:
 
@@ -4215,6 +4215,7 @@ mjs_nextChild
 .. mujoco-include:: mjs_nextChild
 
 Return body's next child of the same type; return NULL if child is last.
+If recurse is nonzero, also search the body's subtree.
 
 .. _mjs_firstElement:
 

doc/includes/references.h

@@ -3598,8 +3598,8 @@ mjsDefault* mjs_getDefault(mjsElement* element);
 mjsDefault* mjs_findDefault(mjSpec* s, const char* classname);
 mjsDefault* mjs_getSpecDefault(mjSpec* s);
 int mjs_getId(mjsElement* element);
-mjsElement* mjs_firstChild(mjsBody* body, mjtObj type);
-mjsElement* mjs_nextChild(mjsBody* body, mjsElement* child);
+mjsElement* mjs_firstChild(mjsBody* body, mjtObj type, int recurse);
+mjsElement* mjs_nextChild(mjsBody* body, mjsElement* child, int recurse);
 mjsElement* mjs_firstElement(mjSpec* s, mjtObj type);
 mjsElement* mjs_nextElement(mjSpec* s, mjsElement* element);
 void mjs_setBuffer(mjByteVec* dest, const void* array, int size);