Simplify some annotation() calls in examples.

TextWithDash appears to be an ancestral version of Annotation that was
added over two commits in 2005 (6a4d343, fe80816), revised once in 2006
and another time in 2008, and never touched since then.

While it "works", its implementation is 400 lines long, it is only
mentioned by a single example (dashpointlabel.py), somewhat complicates
Axes.text(), and is likely rarely used and replaceable by Annotation for
most use cases.

Hence, deprecate it, keeping open the option to undeprecate if this
turns out to be too disruptive.

 Modified docstring of the set_ylabel and set_xlabel

Separate alpha and rbg interpolation then recombine to fix issue11316

Improve GridSpec doc

This caught two "incorrect" tests:

- in test_style.py::test_invalid_rc_warning_includes_filename, the
  `for w in warns: ...` assertion did nothing as no warning was
  emitted so `warns` was empty (instead, the message is just print()ed
  to stderr.
- in test_image.py::test_empty_imshow, the caught warning message was
  missing spaces around the equals.

Cleanup warnings handling in tests.

Strip out Py2-compat in setupext.

FIX: inverted colorbar ticks

Cleanup docs for GraphicsContextBase.{get,set}_dashes.

… label (#13551)

* FIX: legend crashes when bar chart is empty with label

* add test with generating legend with empty bar chart

* remove image_comparison from legend test case

* added function to check if a point lies on a segment

* check if collinear segments have common points in segments_intersect

* test cases added for Path.intersects_path

* PEP8 check

* added a test case for a range of slopes of intersecting paths

* changed the way segments are compared provided their slopes and intercepts match

* typo fix

* simplified logic of segments_intersect when handling the infinite slope case

* implemented isclose for path intersect check; added more test cases

* removed debug include

* flake8 fixes

* typo fix

Co-Authored-By: TarasKuzyo <kuzyo.taras@gmail.com>

* reduced the number of checks to 30 angles and 4 eps values

Small cleanups.

in Poly3DCollection's set_alpha method, facecolor was getting updated when facecolors3d should have been updated instead.

added property  usemathtext to EngFormatter

…ke8 checks pass.

Deprecate redundant log-scale transform classes.

``frameon = False`` has *never* worked since its introduction in 2013
due to the buggy implementation that only took it into account if True:

    if frameon:
        original_frameon = self.get_frameon()
        self.set_frameon(frameon)

(despite the doc stating otherwise).  One can also set the facecolor
kwarg or savefig.facecolor rcParam to fully transparent for the same
effect.

… plots are closely related and thus go into one figure.

This change causes the range of all data sets to be computed and
passed to numpy (which in turn uses the total range to compute the
'best' bins).

The existing code 'latches' the bins from the first data set to use
for the rest so this is can still lead to poor binning (if the data
sets are widely different).

closes #8636

Generate Figure method wrappers via boilerplate.py

Remove \mathcircled from mathtext docs following its deprecation.

numpydoc IndexFormatter

numpydoc ListedColormap parameters

as suggested by @eric-wieser

We are no longer tracking if the bins kwarg was passed, but if
it was passed in is an array we should use as the bin edges.

Simplify some internal logic.

The # variants the PyArg formats will raise deprecation warnings in
py38.

https://bugs.python.org/issue8677
https://bugs.python.org/issue36381
python/cpython#12473
python/cpython@d3c72a2

FIX: if bins input to hist is str, treat like no bins

Add new example for plotting a confidence_ellipse

Numpydocify FontManager.findfont()

Consider the following example.

    import matplotlib.pyplot as plt
    plt.rcParams['text.usetex'] = True
    plt.rcParams['text.latex.preamble'] = r'\usepackage{siunitx}'
    plt.rcParams['text.hinting_factor'] = 1
    plt.text(.5, .5, r'$\si{\degree}$')
    plt.text(.5, .4, r'ff\textwon')
    plt.gca().set_axis_off()
    plt.savefig('/tmp/plot.svg')
    plt.savefig('/tmp/plot.pdf')
    plt.savefig('/tmp/plot.png')
    plt.show()

In the svg output, one sees that the \degree and \textwon characters
(which come from a different font that the ff ligature) are now
correctly loaded, *but* at a too small size -- this still needs to be
fixed.
(pdf and png output are unaffected.)

Cleanup FancyArrowPatch docstring

FIX: textpath encoding

MNT: Better MovieWriter init error message

Some more usage of _check_in_list.

MNT: account for cpython deprecations