Fix InvalidProgramException from Seq.collect over a struct seq materialised with List.ofSeq/Seq.toList/Seq.toArray

[T-Gro]

Fixes #20203

open System.Collections.Immutable
// ImmutableArray<_> is a struct that implements seq<'T>
let xs = ImmutableArray.Create(1, 2, 3)
let result = [ yield! xs ]   // or List.ofSeq (Seq.collect id ...)
// before (Release only): System.InvalidProgramException at runtime
// after: works

The comprehension lowering fed a struct (value-type) sub-collection straight into ListCollector/ArrayCollector.AddMany, which expects a reference seq<'T>, and typed the generated try/finally with the original struct body type. That produced invalid IL — a value type where a reference IEnumerable was expected, plus a spurious ldnull stored into a struct local. The struct sub-collection is now coerced (boxed) to seq<'T> and the try/finally result type is unit.

[github-actions]

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Change path	Release notes path	Description
`src/Compiler`	docs/release-notes/.FSharp.Compiler.Service/11.0.100.md	No current pull request URL (#20227) found, please consider adding it