feat: add get_checked_items for query report

[pruthvi145]

When data of an QueryReport is selectable (checkBoxColumn:true in datatable options), we don't have direct way to get selected items like ListView or ReportView.

This PR introduces a method QueryReport.get_checked_items (inspired by ReportView.get_checked_items).

Usage

frappe.query_reports["Your Report"] = {
  get_datatable_options(options) {
    return Object.assign(options, {
      // Add checkbox Column to the datatable
      checkboxColumn: true,
    });
  },
  onload(report) {
    report.page.add_action_item(__("Test"), () => {
      const checked_rows = report.get_checked_items();
      ...
    });
  },
};

no-docs

[codecov]

Codecov Report

Merging #14988 (3f2eee3) into develop (48be725) will decrease coverage by 0.13%.
The diff coverage is 0.00%.

@@             Coverage Diff             @@
##           develop   #14988      +/-   ##
===========================================
- Coverage    53.70%   53.57%   -0.14%     
===========================================
  Files          743      743              
  Lines        64800    64799       -1     
  Branches      5401     5403       +2     
===========================================
- Hits         34803    34718      -85     
- Misses       26710    26776      +66     
- Partials      3287     3305      +18     

Flag	Coverage Δ
ui-tests	46.62% <0.00%> (-0.33%)	⬇️

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[sagarvora]

UI test 2 wasn't stopping, so I cancelled it.