doc: split foreign.rst (#10718) #7

Job	Run time
Coverage (4.14.x)	9m 44s
Coq 8.16.1	8m 48s
Build (macos-latest, 4.14.x)	13m 21s
Create local opam switch (macos-latest, 5)	5m 27s
Build (ubuntu-latest, 4.14.x)	9m 9s
Create local opam switch (macos-latest, 4.14)	5m 29s
MSVC 4.14.0 / windows_x86	10m 0s
Documentation	38s
Build (windows-latest, 4.14.x)	14m 21s
Create local opam switch (ubuntu-latest, 5)	5m 10s
MSVC 4.14.0 / windows_x86_64	9m 50s
Build (ocaml-variants.5.3.0+trunk, ubuntu-latest, true)	2m 4s
Create local opam switch (ubuntu-latest, 4.14)	5m 17s
Format	2m 36s
Build (5.1.x, ubuntu-latest, true)	2m 11s
Build monorepo benchmark docker image	1m 45s
Build (5.1.x, macos-latest, true)	3m 14s
Nix (macos-latest)	1m 54s
Build (4.14.x, macos-13, true)	8m 58s
Nix (ubuntu-latest)	54s
Build (4.13.x, ubuntu-latest, true)	2m 3s
Build (4.08.x, ubuntu-latest, true)	2m 0s
Build (4.04.x, ubuntu-latest, true, true)	5m 5s
Build (4.02.x, ubuntu-latest, true)	4m 25s
	2h 14m 23s

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