place "Garbage Collector" profile track near system stats

The "Garbage Collector" profile track is sorted to the top of the perfetto UI by https://github.com/bazelbuild/bazel/blob/ee72e6ddbcf19db6e4ddf127bde56ca5676de780/src/main/java/com/google/devtools/build/lib/profiler/ThreadMetadata.java#L89. In paticular, it's often useful to examine the GC track in conjunction with the memory tracks. While it's possible to reorganize the tracks in the Perfetto UI, I propose to move the GC track down by the rest of the system stats by default.

Start in src/main/java/com/google/devtools/build/lib/profiler/ThreadMetadata.java around line 89, where the profile track ordering is defined. Inspect how the "Garbage Collector" track is positioned relative to the system and memory tracks, then verify that the default Perfetto view places it with the system statistics while preserving the other track ordering.

Written by the indexing model from the issue text.