Rely on upstream Merlin analyses

[voodoos]

This brings together changes from #1366, #1367 and #1375.

We now rely on merlin-lib implementations for inlay-hint and signature help.

[coveralls]

Pull Request Test Coverage Report for Build 4568

Details

• 11 of 14 (78.57%) changed or added relevant lines in 3 files are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage decreased (-0.01%) to 21.92%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
ocaml-lsp-server/src/inference.ml	2	3	66.67%
ocaml-lsp-server/src/signature_help.ml	0	2	0.0%

Files with Coverage Reduction	New Missed Lines	%
ocaml-lsp-server/src/signature_help.ml	1	0.0%

Totals
Change from base Build 4565:	-0.01%
Covered Lines:	5554
Relevant Lines:	25338

---

💛 - Coveralls

[voodoos]

NIx and windows breakages are due to the switch to ppx_expect 0.17 and are unrelated to that PR.