test: avoid duplicating functionality from base test classes

[vbarua]

• Reuse base R and N type creators
• Standardize on sb from SubstraitBuilder util
• Remove defaultExtensionCollection from tests
• Introduce reusable substraitToCalcite in PlanTestBase

[vbarua]

In the process of doing some other work, I found myself touching a lot of tests. Instead of complicating that PR, I've opted to improve the reuse of the base test classes.

This PR doesn't modify any tests. It primarily removes redundant fields from test classes in favour of reusing fields in the base test classes.

[vbarua]

I opted to use sb for SubstraitBuilder, which felt slightly more descriptive than b. A short-name is useful because when it's used, it's called frequently to build a plan component. A descriptive name like substraitBuilder ends up being noisy.