tocss: Simplify the hugo:vars type handling

Instead of maintaing a list of all CSS units and functions this commit:

* Uses 3 regexps to detect typed CSS values (e.g. `24px`) + properly handle numeric Go types.
* These regexps may have some false positives -- e.g. strings that needs to be quoted.
* For that rare case, you can mark the string with e.g. `"32xxx" | css.Quoted`
* For the opposite case:  `"32" | css.Unquoted`

Updates #10632

common/types/css/csstypes.go

@@ -0,0 +1,20 @@
+// Copyright 2023 The Hugo Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package css
+
+// QuotedString is a string that needs to be quoted in CSS.
+type QuotedString string
+
+// UnquotedString is a string that does not need to be quoted in CSS.
+type UnquotedString string