Reduce allocations for formatting exception stack traces

[HaloFour]

Reduces the number of allocations when formatting exception stack traces.

1. Accepts a CharSequence instead of a String so that an underlying StringBuilder can be passed directly without requiring an intermediate allocation.
2. Reimplements EcsJsonSerializer#formatStackTraceAsArray to use Matcher to iterate over the CharSequence to avoid allocating the ArrayList<String>, String[] and each individual String element.

[apmmachine]

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#### Build stats * Start Time: 2022-04-26T14:42:05.193+0000 * Duration: 8 min 40 sec #### Test stats :test_tube: | Test | Results | | ------------ | :-----------------------------: | | Failed | 0 | | Passed | 198 | | Skipped | 0 | | Total | 198 |

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[eyalkoren]

Thanks for this PR! Please see https://github.com/HaloFour/ecs-logging-java/pull/1 which proposes some further allocation reduction.

[HaloFour]

Thanks for the assist! 😃