RFR: 7902991: fix deprecation warnings generated when compiling with JDK 16. [v3]

[Sergei Ustimenko]

> This PR fixes compilation warnings that fail builds during compilation because of -Werror flag.
> The issues with compilation appear on JDK 16. Warnings that were fixed:
> - warning: [missing-explicit-ctor] class JTRegModuleHelper in exported package java.lang declares no explicit constructors, thereby exposing a default constructor to clients of module java.base
> - SimpleReporter.java:*: warning: [removal] Integer(int) in Integer has been deprecated and marked for removal 
> 
> After the changes build passes.

Sergei Ustimenko has refreshed the contents of this pull request, and previous commits have been removed. The incremental views will show differences compared to the previous content of the PR. The pull request contains one new commit since the last revision:

  7902991: fix deprecation warnings generated when compiling with JDK 16

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Changes:
  - all: https://git.openjdk.java.net/jtreg/pull/15/files
  - new: https://git.openjdk.java.net/jtreg/pull/15/files/9653b2bb..19cdf379

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jtreg&pr=15&range=02
 - incr: https://webrevs.openjdk.java.net/?repo=jtreg&pr=15&range=01-02

  Stats: 0 lines in 0 files changed: 0 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jtreg/pull/15.diff
  Fetch: git fetch https://git.openjdk.java.net/jtreg pull/15/head:pull/15

PR: https://git.openjdk.java.net/jtreg/pull/15