testMode() method for BaseBuilder

[michalsn]

Description
This PR introduces a new testMode variable that is meant to be used in the testing environment. It replaces all occurrences of $returnSQL, $test and $testing - reducing the number of parameters in a couple of methods.

Important
This should be considered as a BC change since some parameters from methods are removed. Those parameters weren't well documented but there is still a chance that somebody was using them.

Checklist:

• Securely signed commits
• Component(s) with PHPdocs
• Unit testing, with >80% coverage
• User guide updated
• Conforms to style guide

[MGatner]

I'm super excited to see this happening!

[jim-parry]

@MGatner @lonnieezell Is this something we want in RC.2? I figure it's now or after 4.0.0, given the BC

[lonnieezell]

I'm all for it happing now.

[jim-parry]

Lookihng good, and simpler :)
Is this ready to go?

[tangix]

My concern with this is that it won't be possible to (easily) return the actual SQL to do last-minute manipulation (for example inserting stuff that is not in the QB natively) but maybe this is OK?
I use the returned SQL string to insert SQL_CALC_FOUND_ROWS and ON DUPLICATE KEY UPDATE for example.

[michalsn]

@tangix we have a bunch of methods from the getCompiled* family at our disposal.

https://codeigniter4.github.io/userguide/database/query_builder.html?highlight=getcompiled#CodeIgniterDatabaseBaseBuilder::getCompiledSelect

[tangix]

@tangix we have a bunch of methods from the getCompiled* family at our disposal.

Yeah, I guess.