pdl: Update getter names as per C-GETTER

The Rust API Guidelines say that getters should not be prefixed with
‘get_’ in most cases[1].

[1]: https://rust-lang.github.io/api-guidelines/naming.html#getter-names-follow-rust-convention-c-getter

Test: atest pdl_rust_generator_tests_{le,be} pdl_tests
Change-Id: If47c2f032b57075e17f803ae036ea5fb435afad3