JIT: protect delegate invoke with a NoGC region

[EgorBo]

Fixes#105082.

 G_M4108_IG04: ; bbWeight=1, gcrefRegs=0004 {x2}, byrefRegs=0000 {}, byref
mov w1, w0
+ ;; size=4 bbWeight=1 PerfScore 0.50+G_M4108_IG05: ; bbWeight=1, nogc, extend
ldp x0, x2, [x2, #0x10]
; gcrRegs -[x2] +[x0]
blr x2 // code for System.Action`1[int]:Invoke(int):this
; gcrRegs -[x0]
+ ;; size=8 bbWeight=1 PerfScore 5.00+G_M4108_IG06: ; bbWeight=1, extend+ nop

-Defining interruptible range: [0xc, 0x40).+Defining interruptible range: [0xc, 0x38).+Defining interruptible range: [0x3c, 0x44).

[azure-pipelines]

Azure Pipelines:
Successfully started running 5 pipeline(s).
11 pipeline(s) were filtered out due to trigger conditions.
There may be pipelines that require an authorized user to comment /azp run to run.

[dotnet-policy-service]

Tagging subscribers to this area: @JulieLeeMSFT, @jakobbotsch
See info in area-owners.md if you want to be subscribed.

[azure-pipelines]

Azure Pipelines:
Successfully started running 5 pipeline(s).
11 pipeline(s) were filtered out due to trigger conditions.
There may be pipelines that require an authorized user to comment /azp run to run.

[Copilot]

🟡 Changes recommended

The behavioral JIT fix lacks regression coverage for the GC-liveness invariant.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Pull request overview

Fixes a JIT GC-liveness issue by keeping collectible delegates alive through invocation.

Changes:

• Exposes the delegate node during lowering.
• Inserts GT_KEEPALIVE before fully interruptible delegate calls.

File summaries

File	Review
src/coreclr/jit/lower.h	Updates the lowering signature.
src/coreclr/jit/lower.cpp	Extends delegate GC lifetime through invocation. A focused regression test is required.

Review details

• Files reviewed: 2/2 changed files
• Comments generated: 1
• Review effort level: Balanced

[Copilot]

🟡 Changes recommended

The critical delegate-target coverage gap must be fixed before approval.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Review details

Suppressed comments (1)

src/coreclr/jit/lower.cpp:6550

• This GC-correctness change has no regression test even though the linked issue provides a compact repro and the failure can be exercised by making the caller fully interruptible under GC stress. Please add a JIT regression test using a collectible delegate so CI protects the target-load/call boundary and the excluded CFG/tailcall variants.

 BlockRange().InsertBefore(call, new (m_compiler, GT_START_NONGC) GenTree(GT_START_NONGC, TYP_VOID));
call->gtCallMoreFlags |= GTF_CALL_M_ENDS_NOGC_REGION;

• Files reviewed: 3/3 changed files
• Comments generated: 1
• Review effort level: Balanced