Use atomic_refcell instead of parking_lot for wasm32 targets (#1404)

Closes https://github.com/emilk/egui/issues/1401

Cargo.lock

@@ -203,6 +203,12 @@ dependencies = [
  "system-deps",
 ]
 
+[[package]]
+name = "atomic_refcell"
+version = "0.1.8"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "73b5e5f48b927f04e952dedc932f31995a65a0bf65ec971c74436e51bf6e970d"
+
 [[package]]
 name = "atty"
 version = "0.2.14"
@@ -987,7 +993,6 @@ dependencies = [
  "epi",
  "glow",
  "image",
- "parking_lot 0.12.0",
  "poll-promise",
  "rfd",
 ]
@@ -1057,7 +1062,6 @@ version = "0.17.0"
 dependencies = [
  "egui",
  "image",
- "parking_lot 0.12.0",
  "resvg",
  "tiny-skia",
  "usvg",
@@ -1086,7 +1090,6 @@ dependencies = [
  "glow",
  "glutin",
  "memoffset",
- "parking_lot 0.12.0",
  "tracing",
  "wasm-bindgen",
  "web-sys",
@@ -1200,6 +1203,7 @@ version = "0.17.0"
 dependencies = [
  "ab_glyph",
  "ahash 0.7.6",
+ "atomic_refcell",
  "bytemuck",
  "cint",
  "criterion",