Refactor opcodes

[rumkin]

I've rewritten Opcodes creation logic what simplified Interpreter and made Opcode object itself easier to use and more informative.

1. Added new Opcode class with fields code and fullName. Class field fullName created for opcodes like PUSH, JUMP, etc. which have similar names. Now this name is calculated only once. Classes are what V8 optimizer loves to use for faster function optimization. Also I protect it from accidental changes with Object.freeze call, so it could be passed anyway without creating of a duplicate. The interface now looks like this:

   class Opcode {
     readonly code: number
     readonly name: string
     readonly fullName: string
     readonly fee: number
     readonly isAsync: boolean
     // ...
   }

2. Added createOpcodes factory into lib/evm/opcodes.ts. It simplified Interpreter#lookupOpInfo() and removed recalculation and recreation of opcode objects. Due to opcode is always same for same hardfork, so there is no reason to recreate it in runtime on each VM step.
3. To preserve backward compatibility I reconstructed old Opcode object in the Interpreter#_runStepHook() method. This code should be removed in the next major release and replaced with a regular Opcode instance, it will reveal all the benefits of this PR.
   Now it is:

   {
     //...
     opcode: {
       name: opcode.fullName,
       fee: opcode.fee,
       isAsync: opcode.isAsync,
     },
     //...
   }

   And should become:

   {
     //...
     opcode,
     //...
   }

[codecov]

Codecov Report

Merging #659 into master will increase coverage by 0.08%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #659      +/-   ##
==========================================
+ Coverage    91.4%   91.48%   +0.08%     
==========================================
  Files          31       31              
  Lines        1978     1997      +19     
  Branches      326      322       -4     
==========================================
+ Hits         1808     1827      +19     
  Misses         90       90              
  Partials       80       80

Flag	Coverage Δ
#vm	91.48% <100%> (+0.08%)	⬆️

Impacted Files	Coverage Δ
lib/evm/opcodes.ts	100% <100%> (ø)	⬆️
lib/evm/interpreter.ts	98.21% <100%> (-0.28%)	⬇️

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