This change does replacement of ARIA roles that have newer synonyms.
There are a number of newer ARIA roles that are synonyms for older
roles. https://wpt.fyi/results/wai-aria/role/synonym-roles.html has a
number of subtests which expect that when retrieving the value of an
explicitly- specified role attribute, if the value is one of the older
role values, implementations must replace that with its newer synonym.
Additionally: For “img” elements with empty “alt” attributes, change the
default role to the newer, preferred “none” synonym for the older
“presentation” role; import https://wpt.fyi/results/html-aam/roles.html
(which provides test/regression coverage for these changes).
This change separates the steps for checking the string value of the
ARIA “role” attribute out from the element.role_or_default() function
into a separate function — in order to expose a way to just check if the
ARIA “role” attribute actually has a value, without also then computing
a default role value if no “role” attribute value was found.
Otherwise, without this change, the only available function for
retrieving ARIA role values is the element.role_or_default() function —
which always does the additional step of computing (and returning) a
default role value if no “role” attribute is found.
We are currently constructing the attribute names as FlyStrings every
time we invoke one of the ARIA attributes getters/setters. If there are
not any other instances of these strings in-memory, then we're thrashing
the FlyString cache.
Instead, let's follow suit of all other Web attributes - use an x-macro
to generate the attribute names.
