[Modal] Add --calcite-modal-content-padding CSS Variable

[macandcheese]

Description

We recently deprecated the noPadding property on Modal: https://developers.arcgis.com/calcite-design-system/components/modal/#component-api-properties-noPadding

The deprecation message states to use --calcite-modal-padding - which we also deprecated (correctly, since this affected padding in every element of the Modal).

We need to introduce a --calcite-modal-content-padding (or -spacing, whatever the pattern is for other instances like this, for instance in calcite-block), that lets folks re-create the noPadding functionality (or otherwise affect this padding), that is scoped just to the content slot.

Acceptance Criteria

A --calcite-modal-content-padding/spacing CSS Variable is added to calcite-modal that correctly lets folks migrate away from the deprecated noPadding property.

Relevant Info

No response

Which Component

Modal

Example Use Case

No response

Esri team

Calcite (design)

[driskull]

@macandcheese is this one is installed already?

[macandcheese]

Yerp #6078

[github-actions]

Installed and assigned for verification.

[geospatialem]

Verified in beta.99 with the following css:

calcite-modal {
  --calcite-modal-content-padding: 2rem;
}