[MLGO] Use double comparison facilities for reg alloc scoring tests (#88862)

This patch switches from using direct equality (ASSERT_EQ) to the
floating point comparison facilities (ASSERT_DOUBLE_EQ) within google
test to avoid weird floating point problems. There is at least one
downstream that maintains a patch for issues cropping up from the direct
equality.


https://gitlab.alpinelinux.org/alpine/aports/-/blob/master/main/llvm17/allocscore.patch