[linker] Add Mono.Cecil.*.Has* checks when comparing methods/types

[linker] Add Mono.Cecil.*.Has* checks when comparing methods/types

* It reduce memory allocations by avoiding the creation of empty
  collections (only used to tell us there's a Count of 0);

* It also speed up execution, less object creation/GC time;

* Patch also remove some double-casts (is + as/cast)