Fixes for ocaml/testsuite/

[mshinwell]

Some of this was done pretty hastily but I think it's a good start. We should probably do something like:

• get the tree in a state where tests can be run
• run the tests
• promote everything (there will be many changes caused by double quotes being put around type names etc)
• fix failures (checking the diff of a particular test if it fails)
• check the whole diff

[mshinwell]

Update: this now contains all fixes to ocaml/testsuite/ from mshinwell/5.2-runtime-wip-main, where except for a few typing tests everything seems to pass.

[mshinwell]

The build system fix (relating to the lib) library relates to Makefile changes made upstream. Instead of trying to port those I've simply written dune rules.

[mshinwell]

This will need splitting for review, #2976 contains the first chunk (and indeed the majority).