Remove type hinting in Controller_Export_Entries

[jakejackson1]

Description

The methods are used by filters/hooks, and any plugin can change the property type. Remove the type hints to stop PHP fatal errors occurring if a different property type is passed. Instead, we'll do additional checks on these properties to see if the data required is present.

Resolves https://github.com/GravityPDF/pdf-for-gravityview/issues/30

Checklist:

• [x] I've tested the code.
• [ ] My code is easy to read, follow, and understand
• [ ] My code follows the accessibility standards.
• [ ] My code has proper inline documentation / docblocks.

Additional Comments

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (f90b279) 93.30% compared to head (d48bcdc) 75.13%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## development #1486 +/- ## ================================================== - Coverage 93.30% 75.13% -18.18% - Complexity 0 2953 +2953 ================================================== Files 57 243 +186 Lines 1464 12882 +11418 Branches 370 370 ================================================== + Hits 1366 9679 +8313 - Misses 90 3195 +3105 Partials 8 8 ```

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