fix: filter images from telemetry render to prevent supportsVision crash (fixes #315729) (#315735)

* fix: filter images from telemetry render to prevent supportsVision crash (fixes #315729)

The sendInvokedToolTelemetry function renders tool results in a
fire-and-forget async call to count tokens. This async render can
outlive the parent PromptRenderer's DI tree, which is disposed after
the parent render completes (PromptRenderer.render() line 133). When
PrimitiveToolResult is instantiated during the telemetry render after
the parent DI is disposed, @IPromptEndpoint resolves to undefined,
causing 'Cannot read properties of undefined (reading supportsVision)'
in PrimitiveToolResult.onImage().

Fix: filter out image data parts before passing content to the
telemetry renderer. Images trigger onImage() which accesses
this.endpoint.supportsVision — the only code path that crashes.
Images contribute ~1 token each in the tokenizer, so the impact on
token counting is minimal.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* fix: make IPromptEndpoint and IAuthenticationService optional in PrimitiveToolResult

Address review feedback from @connor4312: these DI services should not
be expected to be available when PrimitiveToolResult is rendered in the
fire-and-forget telemetry context where the parent DI tree may be disposed.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

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Co-authored-by: vs-code-engineering[bot] <122617954+vs-code-engineering[bot]@users.noreply.github.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Co-authored-by: Bryan Chen <41454397+bryanchen-d@users.noreply.github.com>