ServiceManager: add isDeclared

Most of the time, AIDL services exist in client/service pairs. In this
context, `while(true) getService` or `waitForService` makes sense.
However, for VINTF services, this client/server coupling isn't
guaranteed. A device may or may not have specific hardware. So, now
IServiceManager can tell a client when a server will exist so it will
know if it needs to wait for this service during boot-up. The function
waitForDeclaredService is provided for this.

These functions are generic (not referring to VINTF specifically)
because they may be expanded to include information about APEX services
in the future OR the infrastructure may be made generic to work, if
desired, on system services.

Bug: 141828236
Test: binderStabilityTest, using waitForDeclaredService function
Change-Id: Ia230625e44e1685cc3fa9230ece8f0a25c88585e