String Increments and Php8.5 - release390

[oleibman]

Fix #4600. String incrementation through the ++ operator is deprecated in Php 8.5. Because we make use of that operator to iterate through columns, we are particularly hard hit by that change - unaddressed, it causes over 2,000 errors in our test suite! It is, fortunately, not as difficult as I feared to correct. Replacing the ++ operator with a call to new method StringHelper::stringIncrement in 79 statements scattered over 31 source modules (in src, samples, test, and infra) eliminates all the messages in the test suite. It is possible that others are lurking, but I don't know a systematic way of determining if there are others. We'll stick with this for now, and deal with any others as they show up.

This PR will be applied to the master, release390, and release222 branches. It will not be applied to the release210 or release1291 branches, which will now accept security changes only.

This is:

• a bugfix
• a new feature
• refactoring
• additional unit tests

Checklist:

• Changes are covered by unit tests
  • Changes are covered by existing unit tests
  • New unit tests have been added
• Code style is respected
• Commit message explains why the change is made (see https://github.com/erlang/otp/wiki/Writing-good-commit-messages)
• CHANGELOG.md contains a short summary of the change and a link to the pull request if applicable
• Documentation is updated as necessary

Why this change is needed?

Provide an explanation of why this change is needed, with links to any Issues (if appropriate).
If this is a bugfix or a new feature, and there are no existing Issues, then please also create an issue that will make it easier to track progress with this PR.