Issue #2879533 by lbaran: Improve Charts code documentation

charts.module

...es/charts_api_example/src/Controller/ChartsApiExample.php

modules/charts_c3/src/Charts/C3ChartsRender.php

modules/charts_c3/src/Plugin/chart/CThreeCharts.php

modules/charts_c3/src/Settings/CThree/CThree.php

modules/charts_c3/src/Settings/CThree/ChartAxis.php

modules/charts_c3/src/Settings/CThree/ChartColor.php

modules/charts_c3/src/Settings/CThree/ChartData.php

modules/charts_c3/src/Settings/CThree/ChartDimensions.php

modules/charts_c3/src/Settings/CThree/ChartLabel.php

modules/charts_c3/src/Settings/CThree/ChartTitle.php

modules/charts_c3/src/Settings/CThree/ChartType.php

modules/charts_google/src/Plugin/chart/GoogleCharts.php

...s/charts_highcharts/src/Charts/HighchartsChartsRender.php

modules/charts_highcharts/src/Plugin/chart/Highchart.php

...harts_highcharts/src/Settings/Highcharts/ChartCredits.php

.../charts_highcharts/src/Settings/Highcharts/ChartLabel.php

...charts_highcharts/src/Settings/Highcharts/ChartLegend.php

.../charts_highcharts/src/Settings/Highcharts/ChartTitle.php

...ts_highcharts/src/Settings/Highcharts/DataLabelStatus.php