Fixes PHPDoc @param and @return types for several Converter methods

[caugner]

Description

Fixes PHPDoc @param and @return types for several Converter methods:

• Some methods supposedly expect an int, even though float values make sense.
• Some methods supposedly return a float, even though they return an int.

(Psalm noticed these inconsistencies for me.)

Checklist:

• I have run composer run-script check --timeout=0 and no errors were reported
• The new code is covered by unit tests (check build/coverage for coverage report)
• I have updated the documentation to describe the changes

[coveralls]

Coverage remained the same at 94.633% when pulling 1dee5f3 on caugner:patch-1 into 733f845 on PHPOffice:develop.