Rollup merge of rust-lang#82374 - clehner:licenses, r=joshtriplett

Add license metadata for std dependencies

These five crates are in the dependency tree of `std` but lack license metadata:
- `alloc`
- `core`
- `panic_abort`
- `panic_unwind`
- `unwind`

Querying the dependency tree of `std` is a useful thing to be able to do, since these crates will typically be linked into Rust binaries. Tools show the license fields missing, as seen in rust-lang#67014 (comment). This PR adds the license field for the five crates, based on the license of the `std` package and this repo as a whole. I also added the `repository` and `descriptions` fields, since those seem useful. For `description`, I copied text from top-level comments for the respective modules - except for `unwind` which has none.

I also note that rust-lang#73530 attempted to add license metadata for all crates in this repo, but was rejected because there was question about some of them. I hope that this smaller change, focusing only on the runtime dependencies, will be easier to review.

cc ```@Mark-Simulacrum``` ```@Lokathor```

library/alloc/Cargo.toml

@@ -2,6 +2,9 @@
 authors = ["The Rust Project Developers"]
 name = "alloc"
 version = "0.0.0"
+license = "MIT OR Apache-2.0"
+repository = "https://github.com/rust-lang/rust.git"
+description = "The Rust core allocation and collections library"
 autotests = false
 autobenches = false
 edition = "2018"

library/core/Cargo.toml

@@ -2,6 +2,9 @@
 authors = ["The Rust Project Developers"]
 name = "core"
 version = "0.0.0"
+license = "MIT OR Apache-2.0"
+repository = "https://github.com/rust-lang/rust.git"
+description = "The Rust Core Library"
 autotests = false
 autobenches = false
 edition = "2018"

library/panic_abort/Cargo.toml

@@ -2,6 +2,9 @@
 authors = ["The Rust Project Developers"]
 name = "panic_abort"
 version = "0.0.0"
+license = "MIT OR Apache-2.0"
+repository = "https://github.com/rust-lang/rust.git"
+description = "Implementation of Rust panics via process aborts"
 edition = "2018"
 
 [lib]

library/panic_unwind/Cargo.toml

@@ -2,6 +2,9 @@
 authors = ["The Rust Project Developers"]
 name = "panic_unwind"
 version = "0.0.0"
+license = "MIT OR Apache-2.0"
+repository = "https://github.com/rust-lang/rust.git"
+description = "Implementation of Rust panics via stack unwinding"
 edition = "2018"
 
 [lib]

library/unwind/Cargo.toml

@@ -2,6 +2,8 @@
 authors = ["The Rust Project Developers"]
 name = "unwind"
 version = "0.0.0"
+license = "MIT OR Apache-2.0"
+repository = "https://github.com/rust-lang/rust.git"
 edition = "2018"
 include = [
   '/libunwind/*',