RFR: 8292043: Incorrect decoding near EOF for stateful decoders like UTF-16 [v2]

[Naoto Sato]

> Fixing incorrect state handling with EOF in `StreamDecoder`. There's a `reset()` call to the decoder seeing the EOF before the last `decode()` operation to handle the state correctly. Removing the call should not affect other cases because `reset()` is issued down the execution.

Naoto Sato has updated the pull request incrementally with one additional commit since the last revision:

  Modified the test per review suggestion

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Changes:
  - all: https://git.openjdk.org/jdk/pull/9945/files
  - new: https://git.openjdk.org/jdk/pull/9945/files/24977db2..09846f00

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=9945&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=9945&range=00-01

  Stats: 36 lines in 1 file changed: 22 ins; 0 del; 14 mod
  Patch: https://git.openjdk.org/jdk/pull/9945.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9945/head:pull/9945

PR: https://git.openjdk.org/jdk/pull/9945