Stdlib: is_uploaded_file() VM + LLVM JIT/AOT

[PurHur]

Problem

move_uploaded_file() (#2005) validates upload temp paths via phpc_is_valid_upload_temp, but is_uploaded_file() is not exposed in compiler stdlib. Secure upload handlers need to check tmp paths before moving.

Goal

is_uploaded_file(string $filename): bool on VM, JIT, and AOT — reuse existing upload temp validation (no PHP internal wrappers).

Acceptance

• Returns true only for phpc_upload_* temps under system temp dir
• PHPT compliance + AOT fixture; @group llvm JIT test
• Capability matrix row VM/JIT/AOT yes

Links

• Stdlib: move_uploaded_file for VM (multipart upload reference apps) #2005 move_uploaded_file
• Stdlib: pow, strval, and expanded PHPT specs #6-FileUploadWeb reference app