Closes #8873: Remove the outdated dist subproject

1. Removes the `dist` subproject as it was unused in the main and had
   bitrotted to an unworking state. This was preventing a successful
   `sbt update`, and hence import into some IDEs.
2. Renames the working `dist-bootstrapped` project to `dist` as the
   latter no longer exists.
3. Adds some clarifications to the documentation on testing about
   which tests are run when running `test` vs.
   `dotty-bootstrapped/test`.

Close #8873
Review by @smarter

Author: iamrecursion

build.sbt

@@ -26,7 +26,6 @@ val `scala-compiler` = Build.`scala-compiler`
 val `scala-reflect` = Build.`scala-reflect`
 val scalap = Build.scalap
 val dist = Build.dist
-val `dist-bootstrapped` = Build.`dist-bootstrapped`
 val `community-build` = Build.`community-build`
 
 val sjsSandbox = Build.sjsSandbox

docs/docs/contributing/testing.md

@@ -9,6 +9,17 @@ Running all tests in Dotty is as simple as:
 $ sbt test
 ```
 
+Specifically, `sbt test` runs all tests that do _not_ require a bootstrapped 
+compiler. In practice, this means that it runs all compilation tests meeting 
+this criterion, as well as all non-compiler tests. 
+
+The entire suite of tests can be run using the bootstrapped compiler as follows:
+
+```bash
+$ sbt
+> dotty-bootstrapped/test
+```
+
 There are currently several forms of tests in Dotty. These can be split into
 two categories:
 

project/Build.scala

@@ -1315,14 +1315,10 @@ object Build {
     packArchiveName := "dotty-" + dottyVersion
   )
 
-  lazy val dist = project.asDist(NonBootstrapped)
+  lazy val dist = project.asDist(Bootstrapped)
     .settings(
       packResourceDir += (baseDirectory.value / "bin" -> "bin"),
     )
-  lazy val `dist-bootstrapped` = project.asDist(Bootstrapped)
-    .settings(
-      packResourceDir += ((baseDirectory in dist).value / "bin" -> "bin"),
-    )
 
   implicit class ProjectDefinitions(val project: Project) extends AnyVal {