feat: add Secp256k1 support to solana-web3.js (#12958)

* feat: add secp256k1 instruction

* feat: use buffer-layout for encoding as well

* style: use consistent naming for types

* style: update typings and make program functions static

* fix: attempt to resolve rollup issue

* fix: expose sysvar in typings

* fix: remove decode instruction functionality (for now)

web3.js/flow-typed/keccak.js

@@ -0,0 +1,4 @@
+declare module 'keccak' {
+  // TODO: Fill in types
+  declare module.exports: any;
+}