Move IndexSourceNode to the SPI

[rschlussel]

Description

Move IndexSourceNode to the SPI

Motivation and Context

Move IndexSourceNode to the SPI so it can be used in ConnectorPlanOptimizers and PlanCheckers

Impact

IndexSourceNode is now in the SPI

Test Plan

build

Contributor checklist

• Please make sure your submission complies with our contributing guide, in particular code style and commit standards.
• PR description addresses the issue accurately and concisely. If the change is non-trivial, a GitHub Issue is referenced.
• Documented new properties (with its default value), SQL syntax, functions, or other functionality.
• If release notes are required, they follow the release notes guidelines.
• Adequate tests were added if applicable.
• CI passed.

Release Notes

Please follow release notes guidelines and fill in the release notes below.

== RELEASE NOTES ==

SPI Changes
* Move IndexSourceNode to the SPI