Enforce a limit on the size of ZenModeConfig

If the treshold is exceeded, boot the apps that have created the biggest rules (excluding trusted apps).

Also, use writeString8 for Zen-related parceling. This gives us considerable savings on average (might be slightly bigger for certain fields on non-ASCII charsets -- but even then most of the fields, like package name and rule id, are ~ASCII).

Bug: 387498139
Test: atest ZenModeHelperTest ZenConfigTrimmerTest
Flag: com.android.server.notification.limit_zen_config_size
Change-Id: I4d0359af86f4b491b0723d2078de6626de9dfc85