Use type safe method to get secret and instanceid

[J0WI]

Summary

Getting rid off some more getSystemValue(), see ##35581 for context.

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)

[blizzz]

CI needs #35580, but there might be some tests needing adjustments (didn't check)

[J0WI]

still some failures in https://drone.nextcloud.com/nextcloud/server/26953/9/4 😕

[szaimen]

/rebase

[PVince81]

@J0WI can you rebase? the bot can't rebase on forks

[come-nc]

Failed tests are worrying, cypress is failing and drone nodb has:

There was 1 error:
239	
240	1) Test\Security\VerificationToken\VerificationTokenTest::testTokenSuccess
241	OCP\Security\VerificationToken\InvalidTokenException: 
242	
243	/drone/src/lib/private/Security/VerificationToken/VerificationToken.php:71
244	/drone/src/lib/private/Security/VerificationToken/VerificationToken.php:91
245	/drone/src/tests/lib/Security/VerificationToken/VerificationTokenTest.php:290

[szaimen]

@J0WI nodb failure seems to be related. Also can you please fix the conflicts? Thanks a lot! :)

[come-nc]

There was 1 error:
227	
228	1) Test\Security\IdentityProof\ManagerTest::testGetSystemKeyFailure
229	PHPUnit\Framework\MockObject\IncompatibleReturnValueException: Method getSystemValueString may not return value of type NULL, its declared return type is "string"
230	
231	/drone/src/tests/lib/Security/IdentityProof/ManagerTest.php:233

314	There were 2 failures:
315	
316	1) Tests\Core\Data\LoginFlowV2ServiceUnitTest::testCreateTokens
317	Expectation failed for method name is "getSystemValue" when invoked 2 time(s).
318	Method was expected to be called 2 times, actually called 1 times.
319	
320	2) OCA\Settings\Tests\Mailer\NewUserMailHelperTest::testGenerateTemplateWithPasswordResetToken
321	Expectation failed for method name is "encrypt" when invoked 1 time(s)
322	Parameter 1 for invocation OCP\Security\ICrypto::encrypt('12345:MySuperLongSecureRandomToken', 'recipient@example.com'): string does not match expected value.
323	Failed asserting that two strings are equal.
324	--- Expected
325	+++ Actual
326	@@ @@
327	-'recipient@example.comMyInstanceWideSecret'
328	+'recipient@example.com'
329	
330	/drone/src/apps/settings/lib/Mailer/NewUserMailHelper.php:112
331	/drone/src/apps/settings/tests/Mailer/NewUserMailHelperTest.php:380