Function extract_flags 

pub fn extract_flags(
    program: &Program<'_>,
    line_offsets: &[u32],
    extra_sdk_patterns: &[(String, usize, String)],
    extra_env_prefixes: &[String],
    config_object_heuristics: bool,
) -> Vec<FlagUse>

Entry point: extract feature flag use sites from a parsed program.

Called unconditionally from parse_source_to_module for all parsed files.