* lisp/textmodes/css-mode.el (css-value-class-alist): Add `calc()' as
a completion candidate for several value classes.
(css--value-class-lookup): Return only unique results.
* test/lisp/textmodes/css-mode-tests.el
(css-test-property-values-no-duplicates)
(css-test-value-class-lookup): Update to reflect the above changes.
* lisp/textmodes/css-mode.el (css--property-values): Don't return
duplicate values.
* test/lisp/textmodes/css-mode-tests.el (css-test-property-values):
Take the above into account.
(css-test-property-values-no-duplicates): Test that duplicates aren't
returned by `css--property-values'.
* lisp/textmodes/css-mode.el (css--property-values): Cache computed
values.
* test/lisp/textmodes/css-mode-tests.el (css-test-property-value-cache):
New regression test for the above.
* lisp/textmodes/css-mode.el (css-property-alist): New defconst
holding CSS identifiers and the values they can have.
(css-property-ids): Compute dynamically from `css-property-alist'.
(css-value-class-alist): New defconst holding property value classes
and their values.
(css--property-value-cache): New variable providing a cache for
`css--property-values'.
(css--value-class-lookup): New function for computing a list of values
in a value class.
(css--property-values): New function for computing a list of possible
values for a CSS property.
(css--complete-property-value): New function for completing a property
value.
(css-completion-at-point): Add support for completing property values.
* test/lisp/textmodes/css-mode-tests.el: New file.
