Rolling up PRs in the queue

Closes #14184 (std: Move the owned module from core to std)
Closes #14183 (Allow blocks in const expressions)
Closes #14176 (Add tests for from_bits.)
Closes #14175 (Replaced ~T by Box<T> in manual)
Closes #14173 (Implements Default trait for BigInt and BigUint)
Closes #14171 (Fix #8391)
Closes #14159 (Clean up unicode code in libstd)
Closes #14126 (docs: Add a not found page)
Closes #14123 (add a line to the example to clarify semantics)
Closes #14106 (Pretty printer improvements)
Closes #14083 (rustllvm: Add LLVMRustArrayType)
Closes #13957 (io: Implement process wait timeouts)