Add Context::copy_image (#5533)

* Closes https://github.com/emilk/egui/issues/5424

This adds support for copying images to the system clipboard on native
and on web using `Context::copy_image`.

Cargo.lock

@@ -240,11 +240,14 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "df099ccb16cd014ff054ac1bf392c67feeef57164b05c42f037cd40f5d4357f4"
 dependencies = [
  "clipboard-win",
+ "core-graphics",
+ "image",
  "log",
  "objc2",
  "objc2-app-kit",
  "objc2-foundation",
  "parking_lot",
+ "windows-sys 0.48.0",
  "x11rb",
 ]
 
@@ -1292,6 +1295,7 @@ dependencies = [
  "accesskit_winit",
  "ahash",
  "arboard",
+ "bytemuck",
  "document-features",
  "egui",
  "log",
@@ -2205,6 +2209,7 @@ dependencies = [
  "image-webp",
  "num-traits",
  "png",
+ "tiff",
  "zune-core",
  "zune-jpeg",
 ]
@@ -2311,6 +2316,12 @@ dependencies = [
  "libc",
 ]
 
+[[package]]
+name = "jpeg-decoder"
+version = "0.3.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f5d4a7da358eff58addd2877a45865158f0d78c911d43a5784ceb7bbf52833b0"
+
 [[package]]
 name = "js-sys"
 version = "0.3.72"
@@ -3882,6 +3893,17 @@ dependencies = [
  "syn",
 ]
 
+[[package]]
+name = "tiff"
+version = "0.9.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ba1310fcea54c6a9a4fd1aad794ecc02c31682f6bfbecdf460bf19533eed1e3e"
+dependencies = [
+ "flate2",
+ "jpeg-decoder",
+ "weezl",
+]
+
 [[package]]
 name = "time"
 version = "0.3.36"