Add generic typehints in PHPDoc

[GuySartorelli]

We should add PHPDoc typehints for generics where appropriate, to improve DX and type safety.

Potentially Handy Links

• project board of a fork where we experimented with this
• devsense - Generics in PHP using PHP DocComments
• phpstan - Generics by Examples

Acceptance criteria

• Don’t use phpstan/psalm prefixes (i.e. use @return and @param directly)
• Don't use any conditional return types
• Add generic typehints for all list implementations
• Add generic typehints for injector get(), create(), and any other methods where it would be relevant for injector
  • NOTE: Not for Injectable - i.e. DataObject::create() should just return static which it already does.
• Add generic typehints for methods which return different objects based on a classname that's passed in
  • e.g. GridFieldConfig::getComponentByType()
  • e.g. SapphireTest::objFromFixture()
• spend a little bit of time to see if there are other quick wins we can get by introducing generics.

Notes

• These can be useful for static analysis testing (e.g. via phpstan or psalm) to validate return types are what you expect them to be - we should probably spin off a separate card to implement that. There's some devs internally who have experience with that.
• Once this is merged, we should look at how the API documentation is rendering generics and do a follow card if needed. (see Check how generics are being rendered in API docs api.silverstripe.org#115)

PRs

• ENH Add generic types #11108
• ENH Add generic types silverstripe-admin#1648
• ENH Add generic types silverstripe-asset-admin#1433
• ENH Add generic types silverstripe-assets#584
• ENH Add generic types silverstripe-auditor#67
• ENH Add generic types silverstripe-blog#739
• ENH Add generic types silverstripe-campaign-admin#291
• ENH Add generic types silverstripe-cms#2914
• ENH Add generic types silverstripe-contentreview#220
• ENH Add generic types silverstripe-errorpage#95
• ENH Add generic types silverstripe-graphql#567
• ENH Add generic types silverstripe-lumberjack#137
• ENH Add generic types recipe-cms#79
• ENH Add generic types silverstripe-mfa#524
• ENH Add generic types silverstripe-subsites#554
• ENH Add generic types silverstripe-versioned#431
• ENH Add generic types silverstripe-versioned-admin#319
• ENH Add generic types silverstripe-userforms#1261
• ENH Add generic types silverstripe-session-manager#177
• ENH Add generic types silverstripe-sharedraftcontent#222
• ENH Add generic types silverstripe-sitewidecontent-report#76
• ENH Add generic types silverstripe-ldap#67
• ENH Add generic types silverstripe-realme#128
• ENH Add generic types silverstripe-securityreport#72
• ENH Add generic types silverstripe-spamprotection#108
• ENH Add generic types silverstripe-staticpublishqueue#182
• ENH Add generic types silverstripe-versionfeed#94
• ENH Add generic types silverstripe-gridfieldqueuedexport#94
• ENH Add generic types silverstripe-login-forms#162
• ENH Add generic types silverstripe-textextraction#86
• ENH Add generic types silverstripe-elemental#1131
• ENH Add generic types cwp-agencyextensions#110
• ENH Add generic types cwp-core#130
• ENH Add generic types cwp#336
• ENH Add generic types silverstripe-iframe#77
• ENH Add generic types silverstripe-registry#90
• ENH Add generic types silverstripe-taxonomy#102
• ENH Add generic types silverstripe-externallinks#117
• ENH Add generic types silverstripe-tagfield#277
• MNT Remove unnecessary @var comments silverstripe-reports#172
• ENH Add generic types silverstripe-testsession#87
• MNT Remove unnecessary @var comments silverstripe-config#107
• MNT Remove unnecessary @var comments silverstripe-siteconfig#152
• ENH Add generic types tractorcow-farm/silverstripe-fluent#819
• ENH Add generic types symbiote/silverstripe-advancedworkflow#511
• ENH Add generic types symbiote/silverstripe-queuedjobs#415
• DOC Document added generic types developer-docs#438

[emteknetnz]

I reviewed up to and including recipe-cms

[emteknetnz]

I reviewed up to and including login-forms