Switch the mmodule annotations to --show-single-annotation.

With this change, @CorePlatformApi or @IntraCoreApi on a class doesn't
apply to its members, so we need fewer @hide tags on its
members. DemoSimpleClass and DemoLibartClass have been updated to take
advantage of this.

With both the flag changes and the @hide tags removed, the methods
included in the API stubs for the two demo classes are the same as
before. (The only visible effect of this change on the stubs is that
the methods in the stubs stubs no longer have @hide tags in their
javadoc, but this presumably doesn't matter. The @hide tag on the
class is still there.)

The contents of the following has been verified with this change:
 - out/soong/.intermediates/libcore/mmodules/core_platform_api/core-platform-api-stubs/android_common/stubsDir/libcore/mmodule/libart/DemoLibartClass.java
 - out/soong/.intermediates/libcore/mmodules/intracoreapi/core-intra-stubs/android_common/stubsDir/libcore/mmodule/libart/DemoLibartClass.java
 - out/soong/.intermediates/libcore/mmodules/simple/core-simple-intra-stubs/android_common/stubsDir/libcore/mmodule/simple/DemoSimpleClass.java

Bug: 115745533
Test: `make core-platform-api-stubs core-intra-stubs core-simple-intra-stubs`
Change-Id: Ibf8f3383aeb95a231548470f878c902b3220bda6
8 files changed