Clean up rustc_*/Cargo.toml.

- Sort dependencies and features sections.
- Add `tidy` markers to the sorted sections so they stay sorted.
- Remove empty `[lib`] sections.
- Remove "See more keys..." comments.

Excluded files:
- rustc_codegen_{cranelift,gcc}, because they're external.
- rustc_lexer, because it has external use.
- stable_mir, because it has external use.

compiler/rustc_span/Cargo.toml

@@ -3,18 +3,18 @@ name = "rustc_span"
 version = "0.0.0"
 edition = "2021"
 
-[lib]
-
 [dependencies]
-rustc_serialize = { path = "../rustc_serialize" }
-rustc_macros = { path = "../rustc_macros" }
+# tidy-alphabetical-start
+indexmap = { version = "2.0.0" }
+md5 = { package = "md-5", version = "0.10.0" }
+rustc_arena = { path = "../rustc_arena" }
 rustc_data_structures = { path = "../rustc_data_structures" }
 rustc_index = { path = "../rustc_index" }
-rustc_arena = { path = "../rustc_arena" }
+rustc_macros = { path = "../rustc_macros" }
+rustc_serialize = { path = "../rustc_serialize" }
 scoped-tls = "1.0"
-unicode-width = "0.1.4"
-tracing = "0.1"
 sha1 = "0.10.0"
 sha2 = "0.10.1"
-md5 = { package = "md-5", version = "0.10.0" }
-indexmap = { version = "2.0.0" }
+tracing = "0.1"
+unicode-width = "0.1.4"
+# tidy-alphabetical-end