Add WithPanicHook logger option for panic log tests

[MKrupauskas]

Add a WithPanicHook logger option that allows callers to specify custom behavior besides panicking on Panic/DPanic logs. This is similar to what we already have with the WithFatal hook implemented in #861.

This will make it possible to unit test Panic log cases like the one we had with our periodic runner which was impossible because of unrecoverable panics in another go routine.

Added unit tests and they pass.

$ make test
?       go.uber.org/zap/internal        [no test files]
?       go.uber.org/zap/internal/bufferpool     [no test files]
ok      go.uber.org/zap (cached)
?       go.uber.org/zap/internal/readme [no test files]
ok      go.uber.org/zap/buffer  (cached)
ok      go.uber.org/zap/internal/color  (cached)
ok      go.uber.org/zap/internal/exit   (cached)
ok      go.uber.org/zap/internal/pool   (cached)
ok      go.uber.org/zap/internal/stacktrace     (cached)
ok      go.uber.org/zap/internal/ztest  (cached)
ok      go.uber.org/zap/zapcore (cached)
ok      go.uber.org/zap/zapgrpc (cached)
ok      go.uber.org/zap/zapio   (cached)
ok      go.uber.org/zap/zaptest (cached)
ok      go.uber.org/zap/zaptest/observer        (cached)
ok      go.uber.org/zap/exp/zapfield    (cached)
ok      go.uber.org/zap/exp/zapslog     (cached)
ok      go.uber.org/zap/benchmarks      (cached) [no tests to run]
ok      go.uber.org/zap/zapgrpc/internal/test   (cached)

Closes #1415

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (e5745d6) 98.44% compared to head (7a4359b) 98.44%.
Report is 2 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1416   +/-   ##
=======================================
  Coverage   98.44%   98.44%           
=======================================
  Files          53       53           
  Lines        3527     3531    +4     
=======================================
+ Hits         3472     3476    +4     
  Misses         46       46           
  Partials        9        9           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[abhinav]

Thanks! This makes sense to me.
Will wait for other maintainers for a second review and merge.

CC @r-hang @sywhang

[sywhang]

LGTM. Thanks!

[MKrupauskas]

Thanks for the reviews folks!