[interp] Add more super instructions and other small optimizations (#51273)

[interp] Add more super instructions and other small optimizations (#51273)

* [interp] Replace ldloca + initobj pair with initlocal

We do it in the cprop pass because ldloca removal can enable additional copy propagations.

* [interp] Replace ldloca + ldobj.vt with mov.vt

* [interp] Add superinstructions for multiplication with constant

* [interp] Remove redundant opcode

* [interp] Update indirects count if removing bblock with ldloca

If the var no longer has indirects, we might be able to do cprop through it

* [interp] Refactor ldind/stind opcodes

Remove some unnecessary opcodes. Always do a null check when dereferencing pointers with ldind. Having an unsafe version of this is really useless performance wise and can only be used in very few cases.

* [interp] Add super instructions for ldind/stind with offset

* [interp] Remove opcode for conversion from i8 to i4

It is redundant, we replace it with a MOV_8 which will end up being removed by the cprop pass.