buffer: refactor module.exports, imports

* Move to more efficient module.exports pattern
* Refactor requires
* Eliminate circular dependency on internal/buffer
* Add names to some functions
* Fix circular dependency error in assert.js

PR-URL: #13807
Reviewed-By: Refael Ackermann <refack@gmail.com>

lib/assert.js

@@ -24,7 +24,6 @@ const { compare } = process.binding('buffer');
 const util = require('util');
 const { isSet, isMap } = process.binding('util');
 const { objectToString } = require('internal/util');
-const { Buffer } = require('buffer');
 const errors = require('internal/errors');
 
 // The assert module provides functions that throw
@@ -119,6 +118,7 @@ function areSimilarRegExps(a, b) {
 // barrier including the Buffer.from operation takes the advantage of the faster
 // compare otherwise. 300 was the number after which compare became faster.
 function areSimilarTypedArrays(a, b) {
+  const { from } = require('buffer').Buffer;
   const len = a.byteLength;
   if (len !== b.byteLength) {
     return false;
@@ -131,12 +131,8 @@ function areSimilarTypedArrays(a, b) {
     }
     return true;
   }
-  return compare(Buffer.from(a.buffer,
-                             a.byteOffset,
-                             len),
-                 Buffer.from(b.buffer,
-                             b.byteOffset,
-                             b.byteLength)) === 0;
+  return compare(from(a.buffer, a.byteOffset, len),
+                 from(b.buffer, b.byteOffset, b.byteLength)) === 0;
 }
 
 function isFloatTypedArrayTag(tag) {