Member avatars without canvas (#9990)

* Strict typechecking fixes for Base/Member/Avatar

Update the core avatar files to pass `--strict --noImplicitAny` typechecks.

Signed-off-by: Clark Fischer <clark.fischer@gmail.com>

* Add tests for Base/Member/Avatar

More thoroughly test the core avatar files. Not necessarily the most thorough,
but an improvement.

Signed-off-by: Clark Fischer <clark.fischer@gmail.com>

* Extract TextAvatar from BaseAvatar

Extracted the fallback/textual avatar into its own component.

Signed-off-by: Clark Fischer <clark.fischer@gmail.com>

* Use standard HTML for non-image avatars

Firefox users with `resistFingerprinting` enabled were seeing random noise
for rooms and users without avatars. There's no real reason to use data
URLs to present flat colors.

This converts non-image avatars to inline blocks with background colors.

See https://github.com/vector-im/element-web/issues/23936

Signed-off-by: Clark Fischer <clark.fischer@gmail.com>

* Have pills use solid backgrounds rather than colored images

Similar to room and member avatars, pills now use colored pseudo-elements
rather than background images.

Signed-off-by: Clark Fischer <clark.fischer@gmail.com>

---------

Signed-off-by: Clark Fischer <clark.fischer@gmail.com>
Co-authored-by: Andy Balaam <andy.balaam@matrix.org>

test/components/views/avatars/__snapshots__/MemberAvatar-test.tsx.snap

@@ -0,0 +1,14 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`MemberAvatar matches the snapshot 1`] = `
+<div>
+  <img
+    alt=""
+    class="mx_BaseAvatar mx_BaseAvatar_image"
+    data-testid="avatar-img"
+    src="http://this.is.a.url//placekitten.com/400/400"
+    style="color: pink;"
+    title="Hover title"
+  />
+</div>
+`;