Refactor selects

In order to do less cloning, refactor selects so that all the
soong-visibile structs are immutable to soong and can be reused.

Additionally, refactor how the inner linked list of selects is managed,
so that the append/prepend/replace logic is simpler.

Bug: 323382414
Test: m nothing --no-skip-soong-tests
Change-Id: Iba5d27405decc1b0596590c3e0555daeb044bf9e
6 files changed