Figure.grdview: Pythonic syntax for surftype parameter

[seisman]

This PR improves grdview's -Q option in a more Pythonic way by splitting it into multiple parameters:

• surftype
• dpi
• nan_transparent
• monochrome
• mesh_fill

Address #4208 (comment).

Example

import pygmt

grd_relief = pygmt.datasets.load_earth_relief(resolution="15m", region=[-25, -13, 63.2, 66.7])

args = dict(
    region=[-25, -13, 63.2, 66.7], 
    projection="M?", 
    perspective=(-150, 25),
    cmap="SCM/oleron",
    zsize="1.5c",
    plane="+ggray",
    panel=True,
)

fig = pygmt.Figure()
with fig.subplot(nrows=5, ncols=3, subsize=(5, 5), margins=(1, 0.2)):
    for surftype in ("surface", "mesh", "surface+mesh", "image", "waterfallx", "waterfally"):
        fig.grdview(
            grid=grd_relief,
            frame=["xaf", "yaf", f"WSenZ+t{surftype}"],
            surftype=surftype,
            **args,
        )
    for surftype in ("surface", "mesh", "surface+mesh", "image", "waterfallx", "waterfally"):
        fig.grdview(
            grid=grd_relief,
            frame=["xaf", "yaf", f"WSenZ+t{surftype}"],
            surftype=surftype,
            monochrome=True,
            **args,
        )
    for surtype in ("mesh", "waterfallx", "waterfally"):
        fig.grdview(
            grid=grd_relief,
            frame=["xaf", "yaf", f"WSenZ+t{surftype}"],
            surftype=surftype,
            meshfill="red@50",
            **args,
        )
fig.show()

[weiji14]

Can you add a unit test to ensure that backwards compatibility is preserved when a user passes surftype="c", but did not set nan_transparent=True (which is added in this PR). The output grdview plot should still have NaN transparency.