[llvm] [llvm][CodeGen] avoid repeated interval calculation in window scheduler (PR #132352)

[Hua Tian via llvm-commits]

huaatian wrote:

> @arsenm Do you think it is appropriate to not calculate the register's live interval here, but instead delay the calculation until getInterval() is called, as suggested by @ytmukai？ [#132677 (comment)](https://github.com/llvm/llvm-project/pull/132677#discussion_r2012106361)

We are eagerly looking forward to your suggestions. Thank you! @arsenm

https://github.com/llvm/llvm-project/pull/132352