chore(godeltaprof): decouple pprof builder from delta computation with an interface

[korniltsev]

1. Add a new interface. It is useful for benchmarking and in the next PR will be used for OTLP proto building. The interface is still in internal folder

type ProfileBuilder interface {
	LocsForStack(stk []uintptr) (newLocs []uint64)
	Sample(values []int64, locs []uint64, blockSize int64)
	Build()
}

2. Add a benchmark for delta computation using noopBuilder

[simonswine]

LGTM