RFR: 8244681: Add a warning for possibly lossy conversion in compound assignments [v17]

[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 incrementally with one additional commit since the last revision:

  re-enabled lossy-conversions warnings for jdk.hotspot.agent

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Changes:
  - all: https://git.openjdk.org/jdk/pull/8599/files
  - new: https://git.openjdk.org/jdk/pull/8599/files/4b78b1c5..0b93c284

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=8599&range=16
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=8599&range=15-16

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 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