feat(auto-edits): fix the partial decoration issue when not enough lines in the editor

[hitesh-1997]

Default auto-edits renderer can not render the decorations properly when there are not enough lines in the editor. The PR adds checks if the deocrator can render the decoration properly, and if it cannot do so we don't create any request for it.

Slack Context
Closes: https://linear.app/sourcegraph/issue/CODY-4656/handle-decorations-when-not-enough-lines-in-the-editor

Example from cody-chat-eval repo

Before (partial decoration rendered):

After (decorations will be discarded) - notice discard event on cody by sourcegraph

█ telemetry-v2 recordEvent: cody.autoedit/discarded: {
  "parameters": {
    "version": 0,
    "interactionID": "3ca8f155-1ab9-4b37-ac37-040340fbc1c8",
    "metadata": [
      {
        "key": "otherCompletionProviderEnabled",
        "value": 0
      },
      {
        "key": "triggerKind",
        "value": 1
      },
      {
        "key": "contextSummary.duration",
        "value": 61.69170800000029
      },
      {
        "key": "contextSummary.totalChars",
        "value": 2832
      },
      {
        "key": "contextSummary.prefixChars",
        "value": 979
      },
      {
        "key": "contextSummary.suffixChars",
        "value": 57
      },
      {
        "key": "contextSummary.retrieverStats.diagnostics.suggestedItems",
        "value": 9
      },
      {
        "key": "contextSummary.retrieverStats.diagnostics.positionBitmap",
        "value": 511
      },
      {
        "key": "contextSummary.retrieverStats.diagnostics.retrieverChars",
        "value": 1796
      },
      {
        "key": "contextSummary.retrieverStats.diagnostics.retrievedItems",
        "value": 9
      },
      {
        "key": "contextSummary.retrieverStats.diagnostics.duration",
        "value": 51.03662500000064
      },
      {
        "key": "source",
        "value": 1
      },
      {
        "key": "isFuzzyMatch",
        "value": 0
      },
      {
        "key": "latency",
        "value": 68
      },
      {
        "key": "decorationStats.modifiedLines",
        "value": 1
      },
      {
        "key": "decorationStats.removedLines",
        "value": 0
      },
      {
        "key": "decorationStats.addedLines",
        "value": 4
      },
      {
        "key": "decorationStats.unchangedLines",
        "value": 40
      },
      {
        "key": "decorationStats.addedChars",
        "value": 104
      },
      {
        "key": "decorationStats.removedChars",
        "value": 45
      },
      {
        "key": "decorationStats.unchangedChars",
        "value": 951
      },
      **{
        "key": "discardReason",
        "value": 9
      },**
      {
        "key": "recordsPrivateMetadataTranscript",
        "value": 1
      }
    ],
    "privateMetadata": {
      "otherCompletionProviders": [],
      "languageId": "typescript",
      "model": "fireworks::v1::autoedits-deepseek-lite-default",
      "contextSummary": {
        "strategy": "auto-edits",
        "duration": 61.69170800000029,
        "totalChars": 2832,
        "prefixChars": 979,
        "suffixChars": 57,
        "retrieverStats": {
          "diagnostics": {
            "suggestedItems": 9,
            "positionBitmap": 511,
            "retrieverChars": 1796,
            "retrievedItems": 9,
            "duration": 51.03662500000064
          }
        }
      },
      "id": "3ca8f155-1ab9-4b37-ac37-040340fbc1c8",
      "responseHeaders": {},
      "decorationStats": {
        "modifiedLines": 1,
        "removedLines": 0,
        "addedLines": 4,
        "unchangedLines": 40,
        "addedChars": 104,
        "removedChars": 45,
        "unchangedChars": 951
      }
    },
    "billingMetadata": {
      "product": "cody",
      "category": "core"
    }
  },
  "timestamp": "2025-01-10T09:33:03.486Z"
}

Test plan

Tested on all the cody-chat-eval examples.

[hitesh-1997]

This was redundant and was not getting used anywhere.

[valerybugakov]

Suggested change

	/**
	* Pre-computed information about diff decorations to be applied to lines in the editor
	*/
	private diffDecorationInfo: DiffDecorationInfo | undefined
	/**
	* Pre-computed information about diff decorations to be applied to lines in the editor
	*/
	private diffDecorationInfo: DiffDecorationInfo | undefined

[hitesh-1997]

done

[valerybugakov]

Let's add a new discardReason and emit a discard event here:

Suggested change

	this.decorator = null
	return
	this.decorator = null
	autoeditAnalyticsLogger.markAsDiscarded({
	requestId,
	discardReason: autoeditDiscardReason.noEnoughLines,
	})
	return

[hitesh-1997]

done

[valerybugakov]

Can we untether this check from the decorator's instance so that we don't have to create and dispose of it later if we don't have enough lines?

[hitesh-1997]

yeah the flow doesn't look good that we only create decorator only to dispose it on some condition.
I though about it when first tried to implement this, As per the current implementation, the manager doesn't know the type of decorator it is using and canRenderDecoration should be specific to a decorator, for example image renderer should have issues which our default renderer has, so making it a instance specific method seemed like the right call.
Please let me know if there are any alternate implementation ideas, would be happy to switch to them :)

[hitesh-1997]

@valerybugakov added another transition state, since conflictingDecorations and default-rendere can discard.