Prototype LLVM 15 support

[shaobo-he]

This prototypes SMACK support for LLVM 15 using the LLVM 15.0.6 binary distribution.

Changes include:

• Bump SMACK LLVM version metadata to 15.0.6.
• Update opaque-pointer-sensitive SMACK code paths to use value, global, GEP source/result, or inferred access types instead of pointer element types.
• Update memory region sizing and static initializer handling for LLVM 15 opaque pointer IR.
• Point the sea-dsa submodule at https://github.com/shaobo-he/sea-dsa.git commit 85ef2bd, which is based on upstream dev15 and adds SeaDsa-side opaque pointer field-type recovery.

SeaDsa fork change:

• Stores recovered pointee evidence in FieldType, so type-aware link fields can distinguish opaque ptr values such as ptr<i32> and ptr<double>.
• Infers that evidence in local analysis from globals, functions, allocas, GEP source/result types, load/store uses, PHI/select values, and indirect call uses.
• Adds tests/opaque_ptr_field_types.ll to check recovered field labels in the generated graph.

Validation:

SMACK ./regtest.py
PASSED count: 197
FAILED count: 0
TIMEOUT count: 0
UNKNOWN count: 0

SeaDsa focused test
opaque_ptr_field_types.ll: OutputCheck passed for ptr<i32> and ptr<double>

Note: SeaDsa full lit target could not be run locally because the downloaded LLVM 15 binary package does not include the llvm-lit path referenced by LLVMConfig.cmake.