Optimise build configuration

[alcaeus]

Q	A
Type	improvement
BC Break	no
Fixed issues

Summary

• Simplify usage of build steps to make this more consistent with the master branch
• Fix wrong version number in 4.0 build stage. This resulted in the default MongoDB version (currently 4.0.7) to be used on travis-ci
• Extract coverage to a separate build to speed up build times
• Add builds against all MongoDB versions supported by the PHP driver

This makes the build files for 1.3.x and master more consistent, with master then using this version of the build file and just adding the new code quality stages.

[malarzm]

3.0 and 3.2 are EOLed, is there any reason to test them?

[alcaeus]

The driver still supports them, which is why I added them to the pipeline. I wouldn't go out of my way to support them, but if we can verify that tests pass without additional work then I'm good for it

[jmikola]

One question regarding Xdebug, but LGTM.

[jmikola]

Is this a clever one-liner to rename the xdebug.ini.disabled INI file to xdebug.ini?

Would it make sense to add || echo "xdebug not available" here, as is done in before_install below?

[alcaeus]

Yep, this expands to mv .../xdebug.ini.disabled .../xdebug.ini. In this case, there is no echo as the next line fails the build if xdebug was not found, providing a more detailed message. The mv in before_install disables the xdebug extension if present, printing an info message if it wasn't available to begin with (which is not a failure condition as we don't want it there for most builds).