[LNT] Refactored plot_parameters

Arguments like plot.0=1.2.3 are the same for the pages Graph and Matrix.
The class MatrixDataRequest has been renamed to PlotParameter
The common code has been moved to helper functions assert_field_idx_valid(), load_plot_parameter(), parse_plot_parameters(),parse_and_load_plot_parameters(), parse_mean_parameter().
Renamed graph_parameters and data_parameters to plot_parameters.

--
OS Laboratory. Huawei Russian Research Institute. Saint-Petersburg

Reviewed By: thopre

Differential Revision: https://reviews.llvm.org/D112607

Author: Pavel Kosov