DESKTOP: the Memory, Plan Cache and Session summary strips show when their snapshot was collected (part of #4966)

[erikdarlingdata]

Part of #4966.

Why

A summary strip that draws the newest snapshot gave no sign of when that snapshot was taken. The Memory strip reads the newest snapshot ever, which can fall outside the chart window under it. The Plan Cache and Session strips read the newest point in the window. A reader couldn't tell stale from current.

What changes

• Memory gets a dim "Collected" tile like its neighbors. Plan Cache and Session get an inline dim "Collected:" label and value at the end of the strip.
• The text is the snapshot's collection time in the display zone, to the second (HistoryTime.SnapshotCollected, which wraps the existing CollectionLocal). Empty value: -- for Memory and Plan Cache, N/A for Session.
• PlanCacheSummarySql now also returns MAX(collection_time), and PlanCacheSummary carries it as CollectionTime.
• SessionStatsSql returns the newest collection inside each bucket (latest_collection_time), and SessionStatsPoint.LatestCollectionTime carries it. The strip shows the last bucket's value, the same collection Top Application and Top Host come from, not the bucket's grid time.

Limits

• Databases is the bucket average; Collected is the newest collection, where Top Application and Top Host come from.
• The Lite half is LITE: the surfaces that show the newest snapshot say when it was collected (part of #4966) #5032. The form here matches it: same labels, empty values and time rules.
• No pin outside the existing Plan Cache and Session Stats SQL tests named these strips, and they still pass.

Test plan

• ViewerSnapshotStripCollectedTests: 5 cases (text, zone, empty marker, xaml elements, load wiring, SQL carries the time). Total 5, 0 failed.
• ViewerSnapshotStripCollectedLiveTests: seeds two Plan Cache collections and two Session collections inside ONE 1-minute bucket at off-minute seconds (+10 s, +50 s). Asserts the Plan Cache summary time, that the Session LatestCollectionTime is the newer collection, and that it differs from the bucket time. Also an empty window gives null. Total 1, 0 failed. RED: projecting bucket_start as latest_collection_time fails it. Carries the #1776 own-store marker.
• RED: the mutations (Memory render passes null, Plan Cache element renamed, SQL column renamed) each failed the matching pin.
• Full suite: see REPORT.
• CI-only: nothing here builds WPF objects. The xaml and wiring pins are source-text pins and run on this Mac.

CHANGELOG

SECTION: Fixed
ENTRY: - Viewer summary strips show when their snapshot was collected ([#5038]) - The Memory, Plan Cache and Session Stats summary strips now show the time their snapshot was collected, in the display zone to the second, so a strip drawn from the newest snapshot no longer reads as current when it isn't.
REF: [#5038]: #5038