[DSE] Apply initializes attribute to DSE (#107282)
Apply the initializes attribute to DSE and guard with a flag,
"enable-dse-initializes-attr-improvement".
The attribute support has been landed in:
https://github.com/llvm/llvm-project/pull/84803
The attribute inference will be landed after this PR:
https://github.com/llvm/llvm-project/pull/97373
