test: guard QuickPick interactions against orphaned pickers

[kevineger]

There's been a new batch of flakes pop up (likely due to a change in VS Code or our internal test harness infrastructure). This set of fixes should hopefully fix them.

VS Code uses a single shared <input> element for all QuickPick/InputBox surfaces (command palette, kernel picker, "Remove Server", etc.) and just swaps aria-label/placeholder/title-bar text when the active picker changes. vscode-extension-tester's InputBox.create() returns a handle to whatever picker is on screen with no check that it's the one the caller intended, so any prior step that leaves a picker open silently corrupts every subsequent setText / executeCommand.

This produced two related flake modes seen in our internal probe runs:

1. Orphan picker: a cleanup selectQuickPickItem('Colab CPU') times out against the Remove Server picker; the try/catch swallows the error but the picker stays open. Every subsequent executeCommand sends Ctrl+Shift+P, which is captured by the still-focused picker, and the >command text is typed into its filter instead of being executed. The next test then fails with Notebook editor did not load in time.

2. Picker-switch mid-call: while polling for "Python" in the kernel picker, the active picker on screen flips to Remove Server (e.g. from a cascading error flow); setText('Python') lands on the wrong picker's filter, the test eventually times out, and the failure screenshot shows "Remove Server" with "Python" typed into it.

Fixes:

• pickerIdentity() / pickerIdentityMatches() read the title bar, input aria-label, and placeholder, and check whether the open picker matches a caller-supplied substring.
• selectQuickPickItem, selectQuickPickItemIfShown, hasQuickPickItem, confirmInputBoxWithDefault, and selectQuickPicksInOrder now take an expectedPickerSubstring and skip iterations where the open picker isn't the expected one. This prevents picker-switch-mid-call (mode 2). Call sites pass the substring inline at each call (per go/tott/643: favor DAMP over DRY in tests so each step is self-documenting), e.g. selectQuickPickItem(driver, 'Remove Server', 'Colab CPU').
• dismissAnyOpenInput() presses ESCAPE and waits for the input to disappear; called from the catch branch of the cleanup's Colab CPU selection in test-setup.ts, and prepended to afterEach. Prevents orphan-picker poisoning (mode 1).
• safeExecuteCommand() wraps Workbench.executeCommand with a dismissAnyOpenInput precondition. All e2e callers now use this instead of the raw workbench.executeCommand(...) so "no picker open" is enforced before every command-palette invocation.
• selectQuickPickItem's timeout message now reports the observed picker identity and the QuickPick items it offered, so the next failure points directly at "wrong picker open" or "expected item missing" instead of looking identical to a generic timeout.

src/test/e2e/connect-execute.e2e.test.ts # modified: src/test/e2e/mount-drive.e2e.test.ts # modified:
src/test/e2e/resource-view.e2e.test.ts # modified: src/test/e2e/test-setup.ts

[hjjackyang]

Nice improvements!