Fix handling of dex cache arrays for method types.

- Add support for relocating method type dex cache arrays.
- Add missing call to MethodTypeDexCachePair::Initialize in the
  class_linker.
- Fix alignment calculation for method_types in
  DexCacheArraysLayout.
- Removed unused MethodTypeOffset(uint32_t) method.

Fixes tests with --pic.

Test: make test-art-host
Bug: 30550796

Change-Id: I2bba7228762b9e9834e7659fe62090be78afdfa8