Rollup merge of #45973 - arielb1:fast-path, r=estebank
Rollup merge of #45973 - arielb1:fast-path, r=estebank

avoid the pprust infrastructure in macro expansion

This changes macro expansion to format the path of a macro directly
instead of usng the pprust infrastructure. The pprust infrastructure
tries to perform line-breaking in a slow fashion, which is undesired
when formatting the path of a macro.

This should to speed up expansion by a fair amount (I saw 20% on a
profiler on `rustc_mir`, and 50% of the time marked as "expansion" in
the profiler/time-passes is actually spent loading dependencies).

r? @jseyfried

graydon/rust,GBGamer/rust,aidancully/rust,graydon/rust,graydon/rust,graydon/rust,aidancully/rust,GBGamer/rust,graydon/rust,aidancully/rust,aidancully/rust,GBGamer/rust,aidancully/rust,GBGamer/rust,GBGamer/rust,graydon/rust,aidancully/rust,GBGamer/rust,GBGamer/rust,GBGamer/rust