[v10] Add character count countType: "words" option using Intl.Segmenter

[colinrotherham]

Description

This PR extends #1895 to add character count support for countType: "words" using Intl.Segmenter

  {{ characterCount({
    label: {
      text: "Can you provide more detail?"
    },
    name: "more-detail",
-   maxwords: 200
+   maxlength: 200,
+   countType: "words"
  }) }}

Issues with separator regex

The existing word count behaviour uses /\S+/g to count all consecutive non-whitespace characters

But consider this phrase where hyphens and em-dashes are used as separators:

My mother-in-law—Wait, what?

It matches only 3 words currently:

["My", "mother-in-law—Wait,", "what?"]

Yet using the segmenter with granularity: "word" it matches 6 words:

["My", "mother", "in", "law", "Wait", "what"]

To solve this, but avoid breaking changes:

• Setting countType: "words will use Intl.Segmenter in modern browsers
• Setting maxwords (deprecated) will use the existing word count behaviour

But what about older browsers that lack Intl.Segmenter support?

They'll fall back to the static non-JS text customisable via textareaDescriptionText, for example:

You can enter up to 350 characters

Checklist

• Tested against our testing policy (Resolution, Browser & Accessibility)
• Follows our coding standards and style guide
• CHANGELOG entry

[colinrotherham]

@anandamaryon1 I've added three changelog entries for:

• Improved character count counting
• Custom character count functions
• Rename the character count maxwords option

If you can check please? 🙏