android_sdk: Add nested-track ordering and merging (#6262)

Expose sibling ordering and sibling merging for nested tracks end to
end, from the C SDK high-level ABI through te_macros, the shared lib,
JNI and the Android Java SDK.

- PerfettoTeHlNestedTrackNamed gains sibling_order_rank, child_ordering,
sibling_merge_behavior and a string/integer sibling merge key, with
PERFETTO_TE_HL_CHILD_ORDERING_* and
PERFETTO_TE_HL_SIBLING_MERGE_BEHAVIOR_* constants mirroring the proto
enums.
- te_macros: PERFETTO_TE_NESTED_TRACK_NAMED_ORDERED(NAME, ID, RANK,
ORDERING) and PERFETTO_TE_NESTED_TRACK_NAMED_MERGED(NAME, ID, BEHAVIOR,
KEY_STR, KEY_INT).
- hl.cc: EmitNamedTrack now takes the nested-named struct and emits the
new fields on the TrackDescriptor.
- Java: PerfettoTrack.setSiblingOrderRank() / setChildOrdering() /
setSiblingMergeBehavior() / setSiblingMergeKey(long|String) plus
CHILD_ORDERING_* and SIBLING_MERGE_BEHAVIOR_* constants; the chain
carries parallel arrays through JNI (direct region copies, lengths
validated against the names array).

Rust bindings mirror the struct additions. The example, shared-lib
integration tests and Java host tests cover both features.