Replace usage of SQL_CALC_FOUND_ROWS with separate queries

[sgiehl]

Description:

With MySQL 8.0.17 the SQL_CALC_FOUND_ROWS feature has been deprecated.

To ensure we stay compatible with upcoming MySQL releases, where this might be removed, this PR replaces all usages with separate queries to fetch the count.

Review

• [ ] Functional review done
• [ ] Potential edge cases thought about (behavior of the code with strange input, with strange internal state or possible interactions with other Matomo subsystems)
• [ ] Usability review done (is anything maybe unclear or think about anything that would cause people to reach out to support)
• [ ] Security review done
• [ ] Wording review done
• [ ] Code review done
• [ ] Tests were added if useful/possible
• [ ] Reviewed for breaking changes
• [ ] Developer changelog updated if needed
• [ ] Documentation added if needed
• [ ] Existing documentation updated if needed

[michalkleiner]

I can't see it from the PR itself — how is the change around the headers related to the SQL_CALC_FOUND_ROWS?

[sgiehl]

The API does not return the count directly but sends it with a header. The changes are only to make that header testable in the API tests.