Fix delta null/zero handling and adjust neutral symbol

[hughess]

Description

Changes delta neutral symbol from en dash to em dash when symbolPosition=left

This helps with BigValue values where positive values could be confused for negative values.

A better long-term solution is needed for this, but putting this in as a short term fix.

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Latest commit: 63dc7ef

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 4 packages

Name	Type
@evidence-dev/core-components	Patch
@evidence-dev/evidence	Patch
@evidence-dev/components	Patch
evidence-test-environment	Patch

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[archiewood]

Also could: make it bold -

Use a thicker dash: e.g. U+2796

[hughess]

Added fix for null and 0 values which were erroring out in the Delta component.

0 values will appear as 0 (or however the user chooses to format them) and nulls will appear as - to maintain consistency with null treatment elsewhere.

There's likely a better way to handle nulls (N/A, null symbol, dashes of various types), and it might need to be configurable depending on the situation. Leaving it for now, so we can tackle it in the same way across the product.