Fix PS backend

[couet]

In TPostScript (like in TPDF) the color should be set in the file only when something painted.

The previous version of TPostScript set the color to many times and the following macro produced a very large file:

void large_ps()
{
    auto c1 = new TCanvas("c1","c1",500,500);
    auto box = new TBox(0.1,0.1,0.9,0.9);
    box->SetFillColor(kYellow);
    box->SetFillStyle(1001);
    c1->Add(box);

    TPostScript ps1("large.ps");

    for (int n = 0; n < 1000000; ++n) {
       gVirtualPS->SetFillColor(kRed);
       gVirtualPS->SetLineColor(kGreen);
    }
    c1->Draw();
    ps1.Close();
}

[linev]

There are still many tests in stressGraphics failing.

I recommend fix also TPostScript::SetLineWidth() and TPostScript::SetLineStyle() and then adjust stressGraphics.ref files. Otherwise one need do same job twice.

[couet]

I know...

[couet]

First I will make sure the ref file are ok with colors.

[github-actions]

Test Results

    22 files      22 suites   3d 1h 10m 32s ⏱️
 3 833 tests  3 832 ✅  1 💤 0 ❌
75 653 runs  75 635 ✅ 18 💤 0 ❌

Results for commit ef7caa4.

♻️ This comment has been updated with latest results.

[linev]

All relevant tests pass so one can merge PR