Support OCaml, Erlang and F# properly

[bbatsov]

Test-at-point rules for erlang-ts-mode and fsharp-ts-mode, plus fuller
project types for all three languages.

Both rules are written against the real grammars, not inferred: the F#
grammar was already installed here, and I installed the Erlang one and parsed
sample sources for both. That's how the F# rule got right that attributes is a
positional sibling of the definition under the enclosing
declaration_expression, rather than a field of it - my first attempt used
treesit-node-child-by-field-name and silently matched nothing.

It also turned up a latent trap in the Rust and Java rules from #2136. Both
tested for their attribute with \_</\_>, which consult the buffer's syntax
table - and under it the < and > of F#'s [<Fact>] count as part of the
symbol, so the boundary never matches. It happened to work for #[test] and
@Test. All three now share one syntax-independent check, with specs for the
bracket forms and for not matching [<Factory>] when looking for Fact.

Erlang addresses a test as module:function and an Erlang module is named after
its file, so the module comes from the file name. F# unwraps a name written
between double backticks, which is how F# tests usually get readable names, and
filters with FullyQualifiedName~ so the filter works without the namespace.

OCaml gets no test-at-point rule, deliberately. Its tests are ordinary values
handed to Alcotest or OUnit - nothing in the syntax marks one out, and dune runtest runs the lot - so any rule would be guesswork dressed up as support.
The effort went into its project type instead: dune exec, dune install,
dune build @install and the source/test directories. rebar gained the same
treatment, and erlang-mk is a new type for the other common Erlang build tool.