Port the test suite to Rust

Federico Mena Quintero requested to merge federico/librsvg:rustify-tests into master

This tries to port all the test suite to Rust (#427 (closed)), except for tests/api.c which test the C API.

Fixes #427 (closed).

It has all of errors/infinite_loop/render_crash/etc. sorted out. I removed some obsolete tests, moved others to the "inline SVG" tests in librsvg_crate where appropriate, and started using the test-generator crate for bulk-testing others.

I'm putting subsets of tests as separate modules under librsvg/tests/src/*.rs just like we had the cmdline ones. @svenfoo is this more or less what you had in mind back then? (If not, the test code is easy to move elsewhere, maybe another binary or something.)

I'm leaving the rsvg-test.c reference tests for the end because those require a bit more work to handle all the special cases.

Edited by Federico Mena Quintero

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