[api-minor] Remove the disableCombineTextItems option

*Please note:* This parameter has never been used within the PDF.js library/viewer itself, and it was only ever added for backwards compatibility reasons.

This parameter was added in PR 7475, over six years ago, to try and optionally maintain the previous *default* text-extraction behaviour.
However as part of the general text-extraction improvements in PR 13257, almost two years ago, the `disableCombineTextItems` functionality was accidentally "broken" in various ways. Note how the only (very basic) unit-test was updated in a way that doesn't really make sense, since generally speaking you'd expect that using the option should result in *more* (or at least the same number of) text-items. Furthermore there's also the recent issue 16209, where the option causes almost all textContent to be concatenated together.

Hence this patch proposes that we simply remove the `disableCombineTextItems` option since it's essentially unused/untested functionality, as evident from the fact that it took almost two years for someone to notice that it's broken.

src/display/api.js

@@ -1120,8 +1120,6 @@ class PDFDocumentProxy {
  * Page getTextContent parameters.
  *
  * @typedef {Object} getTextContentParameters
- * @property {boolean} disableCombineTextItems - Do not attempt to combine
- *   same line {@link TextItem}'s. The default value is `false`.
  * @property {boolean} [includeMarkedContent] - When true include marked
  *   content items in the items array of TextContent. The default is `false`.
  */
@@ -1602,17 +1600,13 @@ class PDFPageProxy {
    * @param {getTextContentParameters} params - getTextContent parameters.
    * @returns {ReadableStream} Stream for reading text content chunks.
    */
-  streamTextContent({
-    disableCombineTextItems = false,
-    includeMarkedContent = false,
-  } = {}) {
+  streamTextContent({ includeMarkedContent = false } = {}) {
     const TEXT_CONTENT_CHUNK_SIZE = 100;
 
     return this._transport.messageHandler.sendWithStream(
       "GetTextContent",
       {
         pageIndex: this._pageIndex,
-        combineTextItems: disableCombineTextItems !== true,
         includeMarkedContent: includeMarkedContent === true,
       },
       {