Shape-verifying reference tests for stroke-linejoin="miter" with miterlimit

[skef]

These two new tests confirm that a miter join with a stroke-miterlimit just above the calculated length is rendered in full and a limit just below the calculated length is rendered as a bevel join. The former test also includes one join with a much larger limit and the latter one join with a much shorter limit.

Most of the joins are formed with straight lines but two in each test are irregular to confirm the browser is calculating the limit from the incoming and outgoing tangent angles alone.

Alterations in style compared with #22791:

First, the last tests were based off a 640x480 grid because earlier tests were scaled from that size. Because those tests evolved to eliminate scaling I've increased width and height to 800 and 600 to match the standard wpt reftest dimensions. This just gives more room for rendering.

Second, those tests were gradually adapted from "fuzzy matching" tests into a non-fuzzy test with an overline. These new tests use the same convention but now it isn't necessary to split all shapes into separate files to avoid "cumulative fuzziness. In trying to follow the spirit of the documentation I've grouped multiple "unclipped" joins into the first test and multiple clipped joins into the second. This way each test is still testing "one thing", just in multiple ways.

Note that I have no strong feelings about any aspect of these particular tests other than I would like, through discussion, to eventually arrive at a mergable test of miter joins with a miterlimit so that I can adapt them into a related set of miterclip tests.

attn @AmeliaBR