[PP-1] Stop installing system module before everything else

Added some hacks which at least show where the problems are:

1. SessionHandler should implement the lazy table creation pattern, then I think batch would work properly.

2. 2005-era spaghetti calls to system_page_attachments() that's never been refactored properly 📌 Remove calls to system_page_attachments() Active

3. The installer uses system_schema() tables to check if Drupal is already installed, that won't work if we have lazy creation. It'll need to check... something else.

4. Minimal install profile depends on system module but doesn't declare a dependency.

With this MR applied, I get the following behaviour - I can click through to profile selection, then after choosing minimal and submitting, I get redirected back to the installer (this is probably lack of working session storage). If I click through again, Drupal tries to install the minimal install profile but chokes on the lack of user module.

We can do #1, #2 and #3 as independent changes in their own issues, without completely reworking the installer, as long as we can find a suitable replacement for #3.

as long as we can find a suitable replacement for #3

How about "does the core.extension config object exist?"

Yes core.extension config object could work!

Opened 📌 Implement lazy database creation for sessions Active .

I have a feeling this will be achievable, or at least attemptable, once 📌 Implement lazy database creation for sessions Active and 📌 Remove calls to system_page_attachments() Active land, so explicitly postponing on those issues.

📌 Implement lazy database creation for sessions Active is in :) (Congrats!)