Towards Wasmi 1.0

[Robbepop]

It's about time!

Before releasing a Wasmi 1.0 we should craft a release with deprecation notes and for 1.0 remove those deprecated definitions.
Furthermore we want to improve Wasmi's Wasmtime API mirror with FuncRef and ExternRef semantic. Also we should finally remove the re-export of the entire wasmi_core crate as submodule and instead re-export only what is needed for wasmi users.
Finally, we want to integrate the new Wasmi translator because it is way simpler to maintain and more efficient.

ToDos

• Wasmi: add new stack based FuncTranslator implementation #1484
• Remove the old register-alloc based Wasmi FuncTranslator #1606
• Remove CopySpan and CopyMany instruction variants #1607
• Remove no longer used BranchTable instruction variants #1608
• Add ConstExprTranslator to remove smallvec dependency #1622
• Remove no longer used wasmi dependencies #1609
• Optimize: op-code fusion of i{32,64}.xor + {br_if,if,select} #1614
• Deprecate wasmi::core crate re-export of wasmi_core crate and re-export user facing items directly from wasmi #1599
• Make ExternRef non-nullable and remove FuncRef #1574
• Deprecation of Module::new_streaming API #1515
• Deprecate LinkerBuilder type #1573
• Deprecate InstancePre type #1572
• Deprecate or redesign StackLimits configuration #1629
• Release Wasmi v0.49.0 including the deprecations above.
  • Prepare release for Wasmi v0.49.0 #1611
• Release Wasmi v0.50.0 including the new FuncTranslator implementation.
  • Prepare release for Wasmi v0.50.0 #1627
• Release Wasmi v0.51.0 including the new stack limits Config API.
  • Prepare release for Wasmi v0.51.0 #1633
• Remove all deprecated items for Wasmi 1.0.0 release #1628