Add stacked chart types to Statistics Graph Card

[TCWORLD]

Proposed change

Allows displaying the entries as stacked lines or stacked bars.

This allows creating statistics charts similar to the energy graph cards but with non-energy entities.

One current limitation is the stacked line chart will not currently show the "now" state because we have no unit conversion so cannot easily guarantee that all entries will be sensible values when stacking them. Easier to just omit that point entirely.

Screenshots

Visual editor supported, simply adds extra options to "Chart type":

Stacked Lines:

Stacked Bars:

For comparison, the existing Bar and Line options:

Type of change

• Dependency upgrade
• Bugfix (non-breaking change which fixes an issue)
• New feature (thank you!)
• Breaking change (fix/feature causing existing functionality to break)
• Code quality improvements to existing code or addition of tests

Additional information

• This PR fixes or closes issue: fixes #
• This PR is related to issue or discussion:
• Link to documentation pull request:
• Link to developer documentation pull request:
• Link to backend pull request:

Checklist

• I understand the code I am submitting and can explain how it works.
• The code change is tested and works locally.
• There is no commented out code in this PR.
• I have followed the development checklist
• I have followed the perfect PR recommendations
• Any generated code has been carefully reviewed for correctness and compliance with project standards.

If user exposed functionality or configuration variables are added/changed:

• Documentation added/updated for www.home-assistant.io

To help with the load of incoming pull requests:

• I have reviewed two other open pull requests in this repository.