Fix #1261: Forward-port additional test for #1252

Originates from: c63d49981b4e7b86e13c4888b3bf680e27bcfdaf which is a
backport commit to 0.5.x that adds an additional test case.
Merge pull request #1264 from gzm0/backport-test

Fix #1261: Forward-port additional test for #1252
Fix #1266: Proper connection closing on Node.js ComJSEnv
Merge pull request #1267 from gzm0/fix-nodejs-race

Fix #1266: Proper connection closing on Node.js ComJSEnv
Fix #1181: Support supplementary chars in RuntimeString.
Merge pull request #1270 from sjrd/fix-supplem-chars-in-runtimestring

Fix #1181: Support supplementary chars in RuntimeString.
Fix #974: Implement java.util.UUID.

Except UUID.nameUUIDFromBytes, because that relies on computing
an MD5 or SHA-1 hash.
Fix #1236: Implement java.io.PrintWriter.
Merge pull request #1273 from sjrd/printwriter

Fix #1236: Implement java.io.PrintWriter.
Implement part of java.nio.{Byte,Char}Buffer.

These are required to implement Charset encoders and decoders.
Merge pull request #1274 from sjrd/uuid

Fix #974: Implement java.util.UUID.
Implement the standard Charset encoders and decoders.

* US-ASCII
* ISO-8859-1
* UTF-8
* UTF-16 BE/LE/auto

This also fixes #1087: String.getBytes().
Fix #1263: Implement java.io.InputStreamReader using CharsetsDecoders.
Merge pull request #1259 from sjrd/charsets

Implement the standard Charset encoders and decoders.
Fix #1276: Do not check sizes for Scala versions not in PR matrix.

Otherwise, they become out-of-sync, and hence completely useless,
pretty easily.
Merge pull request #1279 from sjrd/del-untested-checksizes

Fix #1276: Do not check sizes for Scala versions not in PR matrix.
Make Predef.singleton_<:< and Predef.singleton_=:= inlineable.

Because they are singletons for efficiency, they are not allocated
every time you use them. But then they are not inlineable classes,
and hence did not cause the method call to be inlined, which is a
pity, since their apply method is an identity.

This commit makes any tree of these two types are likely
optimizable. With this, all that remains is a statement loading
the field. We make this elideable as well by noting that
Select(x, y) preserves the pureness of `x`, provided it is not
null. If `x` is a LoadModule(), it cannot be null, so we can
remove it.
Merge pull request #1281 from sjrd/opt-predef-conforms-and-equiv

Make Predef.singleton_<:< and Predef.singleton_=:= inlineable.
Fix some constants in java.lang.Character.
Cleanup java.lang.ThreadLocal.