Add font size traits to various classes

[23ccozad]

Provides users with the ability to change font sizes for various text elements on maps.

Description Of Changes

• Add titlesize trait to MapPanel
• Add clabelsize trait to ContourTraits
• Add colorbar_fontsize trait to ColorfillTraits
• Add font_size trait to PlotObs

Checklist

• Closes Ability to change fontsize in declarative interface #1805
• Tests added
• Fully documented

[kgoebber]

Overall, this PR is looking good. Don't know why it failed on 3.7 minimum requirements...

Thinking a little bit about the naming convention for all of these attributes, I might suggest we go with fontsize (with no underscore for PlotObs and is essentially the standard name), then we can have each thing we set a fontsize for be _fontsize (just as you have for colorbar_fontsize). So that would make the attributes being added in this PR as:

• fontsize
• title_fontsize
• label_fontsize
• colorbar_fontsize

This would bring a reasonable sense of uniformity to the attribute naming convention and would allow us to expand to other fontsizes as needed in the future using the same convention.

[kgoebber]

So the 3.7 minimum PyPI tests are failing due to the minimum Matplotlib being 3.0.1. Some quick testing reveals that this issue is resolved in Matplotlib >=3.2 - don't know what our timeline is for bumping the Matplotlib minimum requirement.

In the meantime we can set the tolerance values separately for the minimum requirement. For example, for the test_declarative_colorbar_fontsize test you could modify the decorator to be:

@pytest.mark.mpl_image_compare(remove_text=False,
                               tolerance={'3.1': 11.49,
                                          '3.0': 11.49}.get(MPL_VERSION, 0.607))

The value of 11.5 for each of the matplotlib versions comes from the RMS result when the test fails. Here are the tolerance values for each of the three new tests.

test_declarative_colorbar_fontsize: 11.49
test_declarative_station_plot_fontsize: 2.12
test_declarative_contour_label_fontsize: 20.3

It turns out that there are some small changes in text placement and on the contour label, it changes the location of the labels in the layout, so that results in a larger RMS.

[23ccozad]

@kgoebber Ryan, Drew, and I came to the same conclusion yesterday, and we'll be moving forward with those changes shortly (on my to-do list today/tomorrow). Then we should be ready for a final review and merge.

[kgoebber]

This PR looks to be in good order now and is a nice addition to the declarative syntax.

[dopplershift]

Nice. Just one style nit and this is ready to go in.

[dopplershift]

I really don't like Python's line continuation characters. How about:

Suggested change

	self.parent.ax.figure.colorbar(self.handle, orientation=self.colorbar,
	pad=0, aspect=50)\
	.ax.tick_params(labelsize=self.colorbar_fontsize)
	cbar = self.parent.ax.figure.colorbar(
	self.handle, orientation=self.colorbar, pad=0, aspect=50)
	cbar.ax.tick_params(labelsize=self.colorbar_fontsize)