This commit improves the compile time of `rustc_platform_intrinsics` from 23s to
3.6s if compiling with `-O` and from 77s to 17s if compiling with `-O -g`. The
compiled rlib size also drops from 3.1M to 1.2M.
The wins here were gained by removing the destructors associated with `Type` by
removing the internal `Box` and `Vec` indirections. These destructors meant that
a lot of landing pads and extra code were generated to manage the runtime
representations. Instead everything can basically be statically computed and
shoved into rodata, so all we need is a giant string compare to lookup what's
what.
Closes#28273
87ede2da54