Improve search addon behavior when there are > 1000 results

[Tyriar]

See microsoft/vscode#178017 for context, _searchResults gets set to undefined when there are > 1000 results:

xterm.js/addons/xterm-addon-search/src/SearchAddon.ts

Lines 168 to 172 in d6599bc

	if (this._searchResults.size > 1000) {
	this.clearDecorations();
	this._resultIndex = undefined;
	return;
	}

[ulgyd0gg]

About the result "0 of -1"

xterm.js/addons/xterm-addon-search/src/SearchAddon.ts

Lines 90 to 101 in d6599bc

	private _updateMatches(): void {
	if (this._highlightTimeout) {
	window.clearTimeout(this._highlightTimeout);
	}
	if (this._cachedSearchTerm && this._lastSearchOptions?.decorations) {
	this._highlightTimeout = setTimeout(() => {
	this.findPrevious(this._cachedSearchTerm!, { ...this._lastSearchOptions, incremental: true, noScroll: true });
	this._resultIndex = this._searchResults ? this._searchResults.size - 1 : -1;
	this._onDidChangeResults.fire({ resultIndex: this._resultIndex, resultCount: this._searchResults?.size ?? -1 });
	}, 200);
	}
	}

this._resultIndex be set to -1, when _searchResults already been set to undefine because of _serachResults.size > 1000 results.

[jeanp413]

Created a PR for it #4504