[Repo Assist] Add trimming support to runtime Core libraries (closes #1436)

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Implements trimming support for all FSharp.Data runtime assemblies, allowing Blazor WASM and other trimmed deployments to reduce bundle size significantly.

Closes #1436

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What changed

IsTrimmable=true added to all runtime Core libraries

The following NuGet packages now declare themselves as trimmable, allowing the .NET trimmer/linker to remove unused code when publishing trimmed applications (e.g. Blazor WASM):

• FSharp.Data.Http
• FSharp.Data.Runtime.Utilities
• FSharp.Data.Json.Core
• FSharp.Data.Csv.Core
• FSharp.Data.Xml.Core
• FSharp.Data.Html.Core
• FSharp.Data.WorldBank.Core

The design-time assembly (FSharp.Data.DesignTime) and the type provider host (FSharp.Data) are intentionally excluded — they only run in the compiler/IDE, not in end-user apps.

Reflection removed from Http.fs

Two reflection call sites were blocking safe trimming:

1. runningOnMono — this let binding used System.Type.GetType "Mono.Runtime" to detect the Mono runtime, but was never actually used anywhere. It has been removed entirely.

2. reraisePreserveStackTrace — previously used typeof(exn).GetField("_remoteStackTraceString", BindingFlags.Instance ||| BindingFlags.NonPublic) to preserve exception stack traces via a private field hack. Replaced with the standard ExceptionDispatchInfo.Capture(e).Throw() API (available since netstandard1.1), which is both trim-safe and semantically superior.

The open System.Reflection import is also removed as it is no longer needed.

Rationale

IsTrimmable=true signals to the .NET trimmer that a library has no unsafe reflection usage and can have unreachable code stripped. Without this flag, the trimmer must preserve the entire assembly to be safe, resulting in significantly larger bundles.

The StructuralTypes.fs/StructuralInference.fs use of typeof(T) is trim-safe — these are compile-time constants, not dynamic lookups.

Test Status

✅ Build succeeded (0 errors, pre-existing warnings only)
✅ Format check passed (fantomas)
✅ All 800 tests passed across FSharp.Data.Core.Tests, FSharp.Data.DesignTime.Tests, FSharp.Data.Tests, and FSharp.Data.Reference.Tests

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