Function find_innermost_scope 

pub fn find_innermost_scope(
    cache: &CompletionCache,
    byte_pos: usize,
    file_id: FileId,
) -> Option<NodeId>

Find the innermost scope node that contains the given byte position and file. scope_ranges must be sorted by span size ascending (smallest first). Returns the node_id of the smallest scope enclosing the position.