feat: clean up nested `match` with `if let`
feat: clean up nested `match` with `if let`

Clean up nested match arms with `if let` and `.is_some()` statements.
Ensure that `generate_struct_field_parse_expression` is called only once.

mthjones/rusoto,DualSpark/rust-aws,DualSpark/rust-aws,mthjones/rusoto,indiv0/rusoto,DualSpark/rusoto,rusoto/rusoto,mattico/rusoto,mattico/rusoto,DualSpark/rust-aws,rusoto/rusoto,DualSpark/rusoto,SecurityInsanity/rusoto,SecurityInsanity/rusoto,ford-prefect/rusoto,rusoto/rusoto,noggleboggle/rusoto,DualSpark/rusoto,ford-prefect/rusoto,cmsd2/rusoto,mattico/rusoto