Unexpected Exception in Php DateTime

[oleibman]

Fix #4696. Fix #917 (which had gone stale but is now reopened). Fix #916. People were receiving unexpected exceptions calling Date::isDateTime($cell). 916 and 917 had been mostly resolved long ago by adding a numeric check on the contents of $cell. However, it turns out that the use of values with very large absolute values can cause Php DateTime to throw an exception, which is the problem with 4696, when it calls Date::exceTolDateTimeObject for a cell with a large integer value.

Date::excelToDateTimeObject is coded to return a Php DateTime object. I don't see any reasonable non-breaking fix for that. People can always add try/catch if they are worried about that. However, Date::isDateTime can add an additional check and return false if this situation occurs. All 3 of the issues resolved by this PR mention isDateTime in their discussion; they are all fixed without additional coding changes by this.

An additional change is needed for Cell::getFormattedValue to avoid this problem. This is fixed in Style::NumberFormatter::DateFormatter::format.

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