RFR: addressing several issues in the implementation of universal tvars [v7]

[Vicente Romero]

> Last review iteration found several issues in the current implementation, addressing them here

Vicente Romero has updated the pull request incrementally with one additional commit since the last revision:

  addressing issues found in last review iteration

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

Changes:
  - all: https://git.openjdk.java.net/valhalla/pull/684/files
  - new: https://git.openjdk.java.net/valhalla/pull/684/files/6722ef71..6ef6c6a3

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=valhalla&pr=684&range=06
 - incr: https://webrevs.openjdk.java.net/?repo=valhalla&pr=684&range=05-06

  Stats: 36 lines in 1 file changed: 5 ins; 23 del; 8 mod
  Patch: https://git.openjdk.java.net/valhalla/pull/684.diff
  Fetch: git fetch https://git.openjdk.java.net/valhalla pull/684/head:pull/684

PR: https://git.openjdk.java.net/valhalla/pull/684