RFR: 8275347 ciReplay: staticfield lines not properly terminated

[Dean Long]

Summary of changes:
- fix staticfield line termination for empty String constants
- tighten up checks during parse time to detect any un-parsed input at the end of a line
- updated test to trigger the problem, so that it fails without the fix
- cleanup: removed _buffer_pos field and related logic that isn't needed

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Commit messages:
 - fix replay line termination

Changes: https://git.openjdk.java.net/jdk/pull/6057/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=6057&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8275347
  Stats: 40 lines in 3 files changed: 24 ins; 7 del; 9 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6057.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6057/head:pull/6057

PR: https://git.openjdk.java.net/jdk/pull/6057