egui_demo_lib: make egui_extras an optional dependency

egui_demo_lib/Cargo.toml

@@ -32,7 +32,7 @@ extra_debug_asserts = ["egui/extra_debug_asserts"]
 # Always enable additional checks.
 extra_asserts = ["egui/extra_asserts"]
 
-http = ["ehttp", "image", "poll-promise"]
+http = ["egui_extras", "ehttp", "image", "poll-promise"]
 persistence = ["egui/persistence", "epi/persistence", "serde"]
 serialize = ["egui/serialize",  "serde"]
 syntax_highlighting = ["syntect"]
@@ -40,7 +40,6 @@ syntax_highlighting = ["syntect"]
 
 [dependencies]
 egui = { version = "0.16.0", path = "../egui", default-features = false }
-egui_extras = { version = "0.16.0", path = "../egui_extras", features = ["image"] }
 epi = { version = "0.16.0", path = "../epi" }
 
 chrono = { version = "0.4", features = ["js-sys", "wasmbind"], optional = true }
@@ -48,6 +47,7 @@ enum-map = { version = "2", features = ["serde"] }
 unicode_names2 = { version = "0.5.0", default-features = false }
 
 # feature "http":
+egui_extras = { version = "0.16.0", path = "../egui_extras", features = ["image"], optional = true }
 ehttp = { version = "0.2.0", optional = true }
 image = { version = "0.24", default-features = false, features = ["jpeg", "png"], optional = true }
 poll-promise = { version = "0.1", default-features = false, optional = true }