Add styling entries in ValoTheme.java for Grid similar to those of Table

Originally by hofmanndavid

Because many will start to move from Table to Grid I guess it will be good to implement all the relevat ValoTheme styling that is already present for Table also for the Grid Component.

Here I show the relevant entries for Table in the ValoTheme.java class that I believe should at least be present as GRID_* styles entries.

_ other Table/TreeTable style.
public static final String TABLE_COMPACT = "compact";
_ Small font size and reduced the white space inside the table cells. Can
_ be combined with any other Table/TreeTable style.
public static final String TABLE_SMALL = "small";
_ Remove the outer border of the table. Can be combined with any other
_ Table/TreeTable style.
public static final String TABLE_BORDERLESS = "borderless";
_ Remove the alternating row colors. Can be combined with any other
_ Table/TreeTable style.
public static final String TABLE_NO_STRIPES = "no-stripes";
_ Remove the vertical divider lines between the table columns. Can be
_ combined with any other Table/TreeTable style.
public static final String TABLE_NO_VERTICAL_LINES = "no-vertical-lines";
_ Remove the horizontal divider lines between the table rows. Can be
_ combined with any other Table/TreeTable style.
public static final String TABLE_NO_HORIZONTAL_LINES = "no-horizontal-lines";
_ Hide the table column headers (effectively the same as
_ {@link ColumnHeaderMode#HIDDEN}). Can be combined with any other
// Table/TreeTable style.
public static final String TABLE_NO_HEADER = "no-header";

Imported from https://dev.vaadin.com/ issue #16937

Start in ValoTheme.java and compare the existing TABLE_* styling constants with the Grid component's supported style names. Add corresponding GRID_* entries for the listed Grid styles, then verify the constants and documentation match the existing Table entries.