fix: detect .svg uris with a query, fragment or upper case extension

[afonsograca]

As a user, I should see an SVG image when its address has a query string or a fragment. Many SVG assets come from a CDN. These addresses often hold a signature or a cache-busting parameter, for example logo.svg?v=1. Today these images are blank.

In this PR we correct the test that finds an SVG address:

• Renderer.image() tested uri.endsWith(".svg"). An address with a query string or a fragment failed this test. The address then went to MDImage. MDImage cannot draw an SVG file, and the image was blank.
• The new test removes the query string and the fragment first. It then compares the extension, and it ignores the letter case. The addresses logo.svg?v=1, LOGO.SVG and logo.svg#top now go to MDSvg.
• We add two tests next to the alt text tests. One test uses https://example.com/logo.svg?v=1. The other test uses https://example.com/LOGO.SVG#top. Both tests use the existing fetch mock, and both tests check that MDSvg renders.
• No snapshot changes. The SVG examples in Markdown.spec.tsx use a plain .svg address.

The predicate is /\.svg$/i.test(uri.split(/[?#]/, 1)[0] ?? ""). The repository sets noUncheckedIndexedAccess, so the index gives string | undefined. The ?? "" gives RegExp.test() a string.

Renderer.image() is the only place that finds an SVG address, so one change is sufficient.

The new tests use the fetch mock that #1089 added.