RFR: JDK-8312395: Improve assertions in growableArray

[Matthias Baesken]

There are a number of assertions in growableArray , for example to check for a valid index to access/remove elements.
Those assertions can be improved, e.g. by showing the bad index value used in case of failure.

Example for an assertion in the 'at(index i)' access method 
old assertion looks like
assert(0 <= i && i < _len) failed: illegal index

new assertion looks like
assert(0 <= i && i < _len) failed: illegal index -559030609, 1 accessible elements

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

Commit messages:
 - JDK-8312395

Changes: https://git.openjdk.org/jdk/pull/14946/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=14946&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8312395
  Stats: 10 lines in 1 file changed: 0 ins; 0 del; 10 mod
  Patch: https://git.openjdk.org/jdk/pull/14946.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14946/head:pull/14946

PR: https://git.openjdk.org/jdk/pull/14946