Add more Rust tests

[Luni-4]

It would be helpful to add tests for Rust grammar starting from this file (v0.19 #552):

• one.zip

[marco-c]

Some that are pretty small to check:

• cache_gecko-dev_third_party_rust_clap_src_app_usage.rs.html
• cache_gecko-dev_servo_components_style_properties_shorthands_column.mako.rs.html
• cache_gecko-dev_toolkit_components_bitsdownload_bits_client_bits_src_wide.rs.html
• cache_gecko-dev_third_party_rust_wio_src_wide.rs.html
• cache_gecko-dev_third_party_rust_lazy_static_tests_no_std.rs.html
• cache_gecko-dev_third_party_rust_error-chain_examples_doc.rs.html
• cache_gecko-dev_third_party_rust_packed_simd_src_v16.rs.html
• cache_gecko-dev_third_party_rust_core-foundation_src_characterset.rs.html
• cache_gecko-dev_third_party_rust_fuchsia-zircon_src_vmar.rs.html
• cache_gecko-dev_third_party_rust_rayon_src_private.rs.html
• cache_gecko-dev_third_party_rust_bitflags_src_example_generated.rs.html
• cache_gecko-dev_third_party_rust_packed_simd_src_v32.rs.html
• cache_gecko-dev_third_party_rust_packed_simd_src_vPtr.rs.html

[Luni-4]

We can use insta tests now

[marco-c]

We can formulate them as insta tests, but we still have to add them.