Make sure frame examples compile for wasm (#5332)

* Make sure frame examples compile for wasm

This makes sure that `frame-example` and `frame-example-offchain-worker`
compile for wasm.

This also fixes compilation for these crates. The offchain worker
example doesn't use serde-json anymore as that is too heavy and breaks
`no_std` compilation.

* Apply suggestions from code review

Co-Authored-By: Nikolay Volf <nikvolf@gmail.com>

Co-authored-by: Nikolay Volf <nikvolf@gmail.com>

substrate/Cargo.lock

@@ -3063,6 +3063,15 @@ dependencies = [
  "linked-hash-map",
 ]
 
+[[package]]
+name = "lite-json"
+version = "0.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "faa835713bb12ba5204013497da16caf2dd2eee25ca829d0efaa054fb38c4ddd"
+dependencies = [
+ "paste",
+]
+
 [[package]]
 name = "lock_api"
 version = "0.3.3"
@@ -4147,9 +4156,9 @@ version = "2.0.0-alpha.4"
 dependencies = [
  "frame-support",
  "frame-system",
+ "lite-json",
  "parity-scale-codec",
  "serde",
- "serde_json",
  "sp-core",
  "sp-io",
  "sp-runtime",
@@ -6718,18 +6727,18 @@ checksum = "f638d531eccd6e23b980caf34876660d38e265409d8e99b397ab71eb3612fad0"
 
 [[package]]
 name = "serde"
-version = "1.0.104"
+version = "1.0.105"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "414115f25f818d7dfccec8ee535d76949ae78584fc4f79a6f45a904bf8ab4449"
+checksum = "e707fbbf255b8fc8c3b99abb91e7257a622caeb20a9818cbadbeeede4e0932ff"
 dependencies = [
  "serde_derive",
 ]
 
 [[package]]
 name = "serde_derive"
-version = "1.0.104"
+version = "1.0.105"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "128f9e303a5a29922045a830221b8f78ec74a5f544944f3d5984f8ec3895ef64"
+checksum = "ac5d00fc561ba2724df6758a17de23df5914f20e41cb00f94d5b7ae42fffaff8"
 dependencies = [
  "proc-macro2",
  "quote",