RFR: 8244681: Add a warning for possibly lossy conversion in compound assignments [v15]

[Adam Sotona]

> Please review this patch adding new lint option, **lossy-conversions**, to javac to warn about type casts in compound assignments with possible lossy conversions.
> 
> The new lint warning is shown if the type of the right-hand operand of a compound assignment is not assignment compatible with the type of the variable.
> 
> The implementation of the warning is based on similar check performed to emit "possible lossy conversion" compilation error for simple assignments. 
> 
> Proposed patch also include complex matrix-style test with positive and negative test cases of lossy conversions in compound assignments.
> 
> Proposed patch also disables this new lint option in all affected JDK modules and libraries to allow smooth JDK build. Individual cases to address possibly lossy conversions warnings in JDK are already addressed in a separate umbrella issue and its sub-tasks.
> 
> Thanks for your review,
> Adam

Adam Sotona has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 19 commits:

 - Merge branch 'openjdk:master' into JDK-8244681
 - re-enabled lossy conversions warnings for java.security.jgss, jdk.crypto.ec and jdk.internal.le
 - Merge branch 'openjdk:master' into JDK-8244681
 - Merge branch 'openjdk:master' into JDK-8244681
 - Merge branch 'openjdk:master' into JDK-8244681
 - re-enabled lossy-conversion javac warnings in JDK Build Tools and jdk.compiler module
 - Added man-page line about lossy-conversion lint
 - Merge branch 'openjdk:master' into JDK-8244681
 - 8244681: Add a warning for possibly lossy conversion in compound assignments
   re-enabled warnings for java.base, java.rmi and java.smartcardio
 - Merge branch 'openjdk:master' into JDK-8244681
 - ... and 9 more: https://git.openjdk.org/jdk/compare/6a1e98cb...4a7ce942

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

Changes: https://git.openjdk.org/jdk/pull/8599/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=8599&range=14
  Stats: 439 lines in 14 files changed: 437 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/8599.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/8599/head:pull/8599

PR: https://git.openjdk.org/jdk/pull/8599