feat: Implement SIP-29 permission and handlers (#3028)

Add an `endowment:assets` permission that lets Snaps expose
`OnAssetsLookup` and `OnAssetsConversion`. These handlers are going to
be called by controllers responsible for managing non-EVM assets. This
PR is mostly adding support for those handlers, as well as the
types/structs required to validate the parameters and responses.
Additionally some work was done to transform the responses to filter out
any out of scope assets returned.

For reference: https://metamask.github.io/SIPs/SIPS/sip-29

---------

Co-authored-by: Maarten Zuidhoorn <[email protected]>

Author: FrederikBolding

packages/examples/packages/browserify-plugin/snap.manifest.json

@@ -7,7 +7,7 @@
     "url": "https://github.com/MetaMask/snaps.git"
   },
   "source": {
-    "shasum": "B0senywfM+w5lQ+iMvK+bVcKJ6VeLDj7HiUVYR5Cuag=",
+    "shasum": "PU8/QaQOlO6/ShRIM+jofaiQFUAprfuUX9RV6G5xRJo=",
     "location": {
       "npm": {
         "filePath": "dist/bundle.js",

packages/examples/packages/browserify/snap.manifest.json

@@ -7,7 +7,7 @@
     "url": "https://github.com/MetaMask/snaps.git"
   },
   "source": {
-    "shasum": "PS0U7SHYXWpFhO8QMtArHKU1rFzMkwtTLFlc3/g1HQ4=",
+    "shasum": "5vUCvHpbE8BnQv9R8QorYcvyKPZk0s+Fuh/MFUZ7LH4=",
     "location": {
       "npm": {
         "filePath": "dist/bundle.js",

packages/snaps-controllers/coverage.json

@@ -1,6 +1,6 @@
 {
-  "branches": 92.96,
-  "functions": 96.56,
-  "lines": 98.05,
-  "statements": 97.77
+  "branches": 93.06,
+  "functions": 96.59,
+  "lines": 98.08,
+  "statements": 97.8
 }