Delay CompatChanges evaluation for CT enabled default value

The default value of CT verification was evaluated as a static final field. The early evaluation caused issues in the `CtsNetSecConfigCertificateTransparencyDefaultSdk36TestCases` test, as it appears the app compat environment was not initialized properly yet.

To fix the problem, `DEFAULT_CERTIFICATE_TRANSPARENCY_VERIFICATION_REQUIRED` was replaced with a function. The function computes the value on demand, and it is now called when the `CompatChanges` initialization is finished.

Bug: 407952621
Test: atest CtsNetSecConfigCertificateTransparencyDefaultSdk36TestCases
Flag: com.android.org.conscrypt.net.flags.certificate_transparency_default_enabled
Change-Id: Ia8fb0606002bee1993994f3d3746bf7c8d98b7b5