stable: cherry-pick for v55.3 (#5964)

- Cherry pick change log update
- Cherry pick proto descriptor relaxation
- Cherry pick gitignore
- Cherry pick all changes in ui/src/plugins/dev.perfetto.HeapProfile and
ui/src/plugins/com.android.HeapDumpExplorer since the last commit in
stable (#5641)

c14f6359e9 ui: Add initial page plumbing (#5869)
5dba463ad4 ui: Add bitmap metadata to the HeapDumpExplorer page (#5861)
b91e5ce379 ui: Control HeapDumpExplorer auto-opening via feature flag
(#5845)
212831ccaf ui: Keep timeline default for native profiles and perf
samples (#5843)
80b19a4841 ui: Stop auto-selecting heap-graph dumps on the timeline
(#5836)
53c4d475f4 ui: Rename HeapDumpExplorer CSS classes from ah- to pf-hde-
(#5830)
d5be6be6a8 ui: Prefix HeapDumpExplorer setting ID with com.android
(#5787)
b63d370819 ui: Default to Heapdump Explorer for traces with heap-graph
data (#5761)
e2b8a81392 ui: Show tooltips on the HeapDumpExplorer columns (#5757)
facb3b4026 ui: Embed flamegraph viewer in Heap Dump Explorer (#5731)
d4061d1507 ui: Extract FlamegraphPanel widget from QueryFlamegraph
(#5730)
4725cd793b ui: Encapsulate plugin state in HeapDumpExplorerSession
(#5679)
fde1f8d625 ui: add matching-slice action to selection flamegraph (#5667)

- To get this to work also cherry-pick be16f77f16 (#5659)
- It is a hard dependency of fde1f8d625 . The "Find matching slices"
action needs openDistributionTab and
sliceDistributionCellRenderers which are defined here.