RFR: addressing several issues in the implementation of universal tvars [v4]

[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:

  removing commented code

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

Changes:
  - all: https://git.openjdk.java.net/valhalla/pull/684/files
  - new: https://git.openjdk.java.net/valhalla/pull/684/files/9e0e224a..a3cc93a2

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=valhalla&pr=684&range=03
 - incr: https://webrevs.openjdk.java.net/?repo=valhalla&pr=684&range=02-03

  Stats: 3 lines in 1 file changed: 0 ins; 3 del; 0 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