Get rid of references to `dotc`

[prolativ]

Currently the command to compile scala 3 code is scalac. The name dotc is not used anymore and should disappear from the documentation unless when it refers to the historical dotc command.

[bishabosha]

I searched through the docs and the only mentions of dotc are in the compiler contribution guide. The reason for that choice being scala 3 compiler is in the package called dotc, like the scala 2 compiler is in the package called nsc. is that not the name of the compiler?

[prolativ]

OK, right - most of the compiler core code resides in dotty.tools.dotc package. However I had an impression that it's just because it would be too much work to migrate the code to use different package names and nobody cared for this enough. Except for this particular context the name dotc seemed to me to be currently out of use. And while I was reading through the contribution guide and came across sentences like

As an example, dotc takes text input, verifies that it is a valid Scala program and then produces as output the same program, but written in Java bytecode ...

I thought that if I were a new contributor to the language I would then expect dotc to be actually a command line program I could run like dotc Foo1.scala to compile my code, which actually used to work in the past but is not valid now.

[bishabosha]

I see now with that snippet in isolation that your comment makes sense. Ok we should identify when the context makes sense to still use dotc (also there's the issue of distinguishing from scala 2 compiler)