Adds ability to find the expressionChainRoot

[TwitchBronBron]

Sometimes plugins need to find the expression at the top of the current chain. For example, doSomething(alpha.beta.charlie) is represented in code as

CallExpression("doSomething", 
  DottedGetExpression("charlie", 
      DottedGetExpression("beta", 
          VariableExpression("alpha")
      )
  )
)

So we want the outer charlie DottedGetExpression because that's the one that is directly held by any parent statement. But in order to detect this, we need to understand ast boundaries, because .parent isn't enough since there's no notion of expression boundaries.

This PR solves that, by providing a .getExpressionChainRoot() function to find the root, or .isExpressionChainRoot property on the node.

• finish tests (look at coverage report to see which functions weren't called yet)
• test this in ropm (the project that actually needs this feature right now).

[rokucommunity-bot]

Hey there! I just built a new temporary npm package based on c9ae549. You can download it here or install it by running the following command:

npm install https://github.com/rokucommunity/brighterscript/releases/download/v0.0.0-packages/brighterscript-0.69.10-get-root-expression.20250613225719.tgz

[rokucommunity-bot]

Hey there! I just built a new temporary npm package based on 1a29e3a. You can download it here or install it by running the following command:

npm install https://github.com/rokucommunity/brighterscript/releases/download/v0.0.0-packages/brighterscript-0.69.10-get-root-expression.20250613225725.tgz

[rokucommunity-bot]

Hey there! I just built a new temporary npm package based on b5a5edb. You can download it here or install it by running the following command:

npm install https://github.com/rokucommunity/brighterscript/releases/download/v0.0.0-packages/brighterscript-0.69.12-get-root-expression.20250725180450.tgz

[rokucommunity-bot]

Hey there! I just built a new temporary npm package based on ccab965. You can download it here or install it by running the following command:

npm install https://github.com/rokucommunity/brighterscript/releases/download/v0.0.0-packages/brighterscript-0.69.13-get-root-expression.20250808160510.tgz

[rokucommunity-bot]

Hey there! I just built a new temporary npm package based on 2b5138e. You can download it here or install it by running the following command:

npm install https://github.com/rokucommunity/brighterscript/releases/download/v0.0.0-packages/brighterscript-0.70.0-get-root-expression.20250812191928.tgz

[rokucommunity-bot]

Hey there! I just built a new temporary npm package based on cea083c. You can download it here or install it by running the following command:

npm install https://github.com/rokucommunity/brighterscript/releases/download/v0.0.0-packages/brighterscript-0.70.0-get-root-expression.20250813125649.tgz