RFR: JDK-8271258: @param with non-ascii variable names produces incorrect results [v2]

[Jonathan Gibbons]

> Please review a simple change to fix the use of non-ASCII characters in @param names.
> 
> The underlying problem was accidentally relying on `DocTree.toString()` for an `IdentifierTree` in `CommentHelper`.  The fix is simply to get the underlying `Name` and call `toString` on that.
> 
> There is some loosely related cleanup in `ParamTaglet`. I did see if it was possible to avoid excessive use of `String` in this part of the code, but that quickly became a rat-hole.
> 
> The existing related test is updated to include this new case, of a Chinese identifier occurring in various places, similar to the test case in the original bug.

Jonathan Gibbons has updated the pull request incrementally with one additional commit since the last revision:

  repair broken test.

-------------

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/5168/files
  - new: https://git.openjdk.java.net/jdk/pull/5168/files/de5e26ef..fc264885

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=5168&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=5168&range=00-01

  Stats: 2 lines in 1 file changed: 0 ins; 1 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5168.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5168/head:pull/5168

PR: https://git.openjdk.java.net/jdk/pull/5168