Auto merge of #54601 - cuviper:prep-1.31, r=Mark-Simulacrum

Bump to 1.31.0 and bootstrap from 1.30 beta

Closes #54594.

diff --cc src/liballoc/lib.rs
Simple merge

diff --cc src/libcore/lib.rs
Simple merge

diff --cc src/libcore/num/mod.rs
Simple merge

diff --cc src/librustc_driver/lib.rs
Simple merge

diff --cc src/librustc_lint/lib.rs
Simple merge

diff --cc src/librustc_privacy/lib.rs
Simple merge

diff --cc src/librustc_resolve/lib.rs
Simple merge

diff --cc src/librustc_save_analysis/lib.rs
Simple merge

diff --cc src/librustc_typeck/lib.rs
Simple merge

diff --cc src/libstd/panicking.rs
Simple merge

diff --cc src/libsyntax_pos/lib.rs
Simple merge