evm: use clean context for GetCommittedState (#383)

* keep the original context for GetCommittedState api

* fix method mutation

* keep estimateGas consistant

* added test after the original context is recovered

* add integration test for the gas consumption of sstore

* test the committed case

* move methods to keeper module

Co-authored-by: Federico Kunze Küllmer <31522760+fedekunze@users.noreply.github.com>

tests/solidity/suites/basic/test/estimateGas.js

@@ -0,0 +1,22 @@
+const Storage = artifacts.require("Storage")
+
+contract('Storage', (accounts) => {
+
+  let storage
+  beforeEach(async () => {
+    storage = await Storage.new()
+  })
+
+  it('estimated gas should match', async () => {
+      // set new value
+      let gasUsage = await storage.store.estimateGas(10);
+      expect(gasUsage.toString()).to.equal('43754');
+
+      await storage.store(10);
+
+      // set existing value
+      gasUsage = await storage.store.estimateGas(10);
+      expect(gasUsage.toString()).to.equal('28754');
+  })
+
+})