This is the following find and replace:

 - `rts/dist` -> `rts/dist-install` # for paths
 - `rts_dist` -> `rts_dist-install` # for make rules and vars
 - `,dist` -> `,dist-install` # for make, just in rts/ghc.mk`

Why do this? Does it matter when the RTS is just built once? The answer
is, yes, I think it does, because I want the distdir--stage
correspondence to be consistent.

In particular, for #17191 and continuing from
d5de970d I am going to make the headers
(`rts/includes`) increasingly the responsibility of the RTS (hence their
new location). However, those headers are current made for multiple
stages. This will probably become unnecessary as work on #17191
progresses and the compiler proper becomes more of a freestanding cabal
package (e.g. a library that can be downloaded from Hackage and built
without any autoconf). However, until that is finished, we have will
transitional period where the RTS and headers need to agree on dirs for
multiple stages.

I know the make build system is going away, but it's not going yet, so I
need to change it to unblock things :).