Clean up css-property-alist for alignment

* css-mode.el (css-property-alist, css-value-class-alist): Provide new
position related entries for use in css-property-alist.  Make sure
that property-alist reflect the spec:
https://www.w3.org/TR/css-align-3/#property-index

lisp/textmodes/css-mode.el

@@ -302,34 +302,25 @@
     ("grid-template-rows" "none" track-list auto-track-list)
 
     ;; CSS Box Alignment Module Level 3
-    ;; (https://www.w3.org/TR/css-align-3/#alignment-values)
-    ("align-content" "center" "start" "end" "flex-start" "flex-end"
-     "normal" "first" "last" "baseline" "space-between" "space-around"
-     "space-evenly" "stretch" "safe" "unsafe")
-    ("align-items" "normal" "stretch" "center" "start" "end"
-     "flex-start" "flex-end" "baseline" "first" "last" "baseline"
-     "safe" "unsafe")
-    ("align-self" "auto" "normal" "center" "start" "end"
-     "self-start" "self-end" "flex-start" "flex-end"
-     "baseline" "first" "last" "stretch" "safe" "unsafe")
-    ("justify-content" "center" "start" "end" "flex-start" "flex-end"
-     "left" "right" "normal" "space-between" "space-around"
-     "space-evenly"  "stretch" "safe" "unsafe")
-    ("justify-items" "auto" "normal" "stretch" "center" "start" "end"
-     "flex-start" "flex-end" "self-start" "self-end" "left" "right"
-     "baseline" "first" "last" "legacy" "safe" "unsafe")
-    ("justify-self" "auto" "normal" "stretch" "center" "start" "end"
-     "flex-start" "flex-end" "self-start" "self-end" "left" "right"
-     "baseline" "first" "last" "safe" "unsafe")
-    ("place-content" "center" "start" "end" "left" "right" "flex-start"
-     "flex-end" "baseline" "first" "last" "space-evenly" "space-around"
-     "space-between")
-    ("place-items" "auto" "normal" "center" "start" "end"
-     "self-start" "self-end" "flex-start" "flex-end"
-     "left" "right" "baseline" "first" "last" "stretch")
-    ("place-self" "auto" "center" "start" "end" "self-start" "self-end"
-     "flex-start" "flex-end" "normal" "left" "right" "baseline"
-     "first" "last" "stretch")
+    ;; (https://www.w3.org/TR/css-align-3/#property-index)
+    ("align-content"
+     baseline-position content-distibution overflow-position content-position)
+    ("align-items"
+     "normal" "stretch" baseline-position overflow-position self-position)
+    ("align-self"
+     "auto" "normal" "stretch"
+     baseline-position overflow-position self-position)
+    ("justify-content" "normal"
+     content-distibution overflow-position content-position "left" "right")
+    ("justify-items"
+     "normal" "stretch" baseline-position overflow-position self-position
+     "left" "right" "legacy")
+    ("justify-self"
+     "auto" "normal" "stretch" baseline-position overflow-position self-position
+     "left" "right")
+    ("place-content" align-content justify-content)
+    ("place-items" align-items justify-items)
+    ("place-self" justify-self align-self)
 
     ;; CSS Flexible Box Layout Module Level 1
     ;; (https://www.w3.org/TR/css-flexbox-1/#property-index)
@@ -779,6 +770,13 @@ further value candidates, since that list would be infinite.")
     (padding-width length percentage)
     (position
      "left" "center" "right" "top" "bottom" percentage length)
+    (baseline-position "left" "right" "baseline")
+    (content-distribution
+     "space-between" "space-around" "space-evenly" "stretch")
+    (overflow-position "unsafe" "safe")
+    (content-position "center" "start" "end" "flex-start" "flex-end")
+    (self-position
+     "center" "start" "end" "self-start" "self-end" "flex-start" "flex-end")
     (radial-gradient "radial-gradient()")
     (relative-size "larger" "smaller")
     (repeat-style