Merge 2.10.x to master

Review by @adriaanm 

The conflict resolution in dist.doc is the main spot to check.

```
export MB=`git merge-base origin/2.10.x origin/master`
merge/2.10.x-to-master ~/code/scala4 git --no-pager  log $MB...origin/2.10.x --oneline --graph
* 9cdbe28 Fixup #3248 missed a spot in pack.xml
*   4aaee3b Merge pull request #3249 from retronym/ticket/7912
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| * 006e2f2  Be defensive calling `toString` in `MatchError#getMessage`
* |   0b77398 Merge pull request #3251 from retronym/ticket/8060
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| * | bb427a3  Avoid infinite loop with higher kinded type alias
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* |   f405417 Merge pull request #3248 from adriaanm/dist-cleanup-licenses
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| * 27a3860 Update README, include doc/licenses in distro
| * 139ba9d Add attribution for Typesafe.
| * e555106 Remove docs/examples; they reside at scala/scala-dist
| * dc6dd58 Remove unused android test and corresponding license.
| * f8d8f7d Do not distribute partest and its dependencies.
* |   0c92704 Merge pull request #3222 from skyluc/issue/completion-import-vals-210-7995
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| * | 5ed834e  completion imported vars and vals
* | |   a444ed7 Merge pull request #3244 from rtyley/si-8019-swing-publisher-check-pf-defined
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| * | c955cf4  Make Publisher check PartialFunction is defined for Event
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* |   db19ddf Merge pull request #3229 from retronym/ticket/8029
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| * | fdcc262  Avoid multi-run cyclic error with companions, package object
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* |   4d439dd Merge pull request #3230 from retronym/backport/7439
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| * | 8d74fa0 [backport]  Avoid NPE in `isMonomorphicType` with stub symbols.
* | |   a774157 Merge pull request #3223 from retronym/ticket/8010-2.10.x
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| * | | 9036f77  Fix regression in erasure double definition checks
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* | |   f6c6846 Merge pull request #3232 from xeno-by/topic/macro-error-messages-210x
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| * | 3faa2ee [nomaster] better error messages for various macro definition errors
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* | 7e996c1 Merge pull request #3209 from dotta/-on-2.10.x
* |   7d74884 Merge pull request #3181 from heathermiller/issue/6913
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| * 7063439  Fixing semantics of Future fallbackTo to be according to docs
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* 7c1d114 Merge pull request #3208 from dotta/si-7548-on-2.10
* 02308c9  Pres. compiler must not observe trees in silent mode
* 652b3b4  Test to demonstrate residual exploratory typing bug
* b7509c9  askTypeAt returns the same type whether the source was fully or targeted type-checked
```