<mark>'s UIA LocalizedControlType and AX AXRoleDescription should be unified

[dandclark]

Per https://w3c.github.io/html-aam/#el-mark, the UIA LocalizedControlType for is "mark" while the AXRoleDescription is "highlighted content". There is no good reason for these values to be different; this adds complexity for implementers and creates confusion for users when moving across platforms. Furthermore, "mark" is a confusing name for non-programmers, and "highlighted content" is unnecessary verbose.

A reasonable fix would be to switch both role descriptions to "highlight", removing the inconsistency and improving upon both existing names.

For context, this came up on this Chromium code review: https://chromium-review.googlesource.com/c/chromium/src/+/1762581