rollup merge of #22191: nagisa/target-ptr-width-json

This aligns json target specification to match terminology used elsewhere in the code base.

[breaking-change] for custom target json users. Change all appearances of target-word-size
to target-pointer-width.

diff --cc src/librustc/session/config.rs
Simple merge

diff --cc src/librustc_back/target/mod.rs
Simple merge