Migrate to the .NET 10 SDK

[nojaf]

Move global.json to 10.0.100 and retarget every net6.0 project to net10.0: the fslex and fsyacc tools, the Expecto test projects and the example projects. The shipped FsLexYacc.targets and the NuGet template now point at build/fslex/net10.0 and build/fsyacc/net10.0, so consumers of the tools package need a .NET 10 runtime.

FSharp.Core 10 — is this reasonable?

@dsyme @T-Gro @baronfel — I'd like a sanity check on one part of this before merging.

This raises the FSharp.Core floor for FsLexYacc.Runtime from >= 4.6.2 to >= 10.1.400. That is a big jump for a package that a lot of people take a transitive dependency on, so I don't want to do it quietly.

My reasoning is that the older versions are no longer usable on the .NET 10 SDK, not merely old:

• 4.6.2 and 4.7.2 make the compiler emit dynamic arithmetic instead of inlining it. The tests fail at runtime with Dynamic invocation of op_Subtraction is not supported, thrown from Position.Column in Lexing.fs — which is a plain int - int.
• 6.0.0 gets past that but breaks dotnet publish with NETSDK1152, because the package ships FSharp.Core.xml under both netstandard2.0 and netstandard2.1 content files and the SDK now rejects the collision.

So the floor has to move; the question is how far. I went to 10 because that is what the compiler repo itself ships and consumes (FSharpCoreShippedPackageVersionValue is 10.0.101 in eng/Versions.props), and picking an intermediate version looked like it would just defer the same conversation.

I think this is fine, but it's a one-way door for anyone still on an older FSharp.Core, so I'd rather ask than assume. If you'd prefer a lower floor that still works, I'm happy to change it.

Everything else

• Local tools bumped. Paket had to move to 10.3.1 because 8.0.3 cannot parse the net10.0 framework identifier at all. Fantomas is on the latest 8.0.0 alpha; it no longer recognises fsharp_max_dot_get_expression_width, renamed the check command, and reformats one call in Lexing.fs.
• FAKE is gone. build.fsx is now a Fun.Build script run with dotnet fsi, and tests/fsyacc/OldFsYaccTests.fsx is a plain dotnet fsi script. Beyond FAKE being fairly quiet these days, it was an active blocker here: FAKE compiles its scripts against the reference assemblies of the framework in the #r "paket:" header, and a runner with only the .NET 10 SDK has no net6.0 targeting pack, so the build died before the first target ran. FAKE's bundled Paket cannot parse net10.0 either, so there was no version of that header that worked.
• build.sh and build.cmd now invoke dotnet fsi build.fsx; pipelines are selected with -p (-p Release, -p Docs) instead of FAKE's -t.
• actions/setup-dotnet bumped to v6; the other actions are already on their latest major.

[T-Gro]

IMO 10 makes the most sense - 8 and 9 are going out of support in a few months.