Implement TransformError/TemplateError subclasses

[noelforte]

Ok! Here's the PR for the errors.ts file. I tried to be as conservative as possible with my edits and did a lot of research on the best way to implement 'default' properties in class declarations in TypeScript. I'm still pretty new to coding in TypeScript so I'm happy to make any corrections or edits if you would prefer things be handled differently.

Some quick notes to summarize things we discussed previously:

• I opted not to expose a code property on TemplateError instances since I think good error tracing can help identify the problem.

• Likewise, I removed redundant logging of the cause message from TemplateError implementations, instead only including a short message with cause.name if it's defined. The TransformError message only adds context about the compiled JS function so I think it's better left in the stack.

  A `TransformError` now looks like this:

  error: Uncaught (in promise) TemplateError: Error in template test.vto:1:1
  
  {{ foo 'alpha', 'beta', 'gamma' }}
  
  (via TransformError)
  
            throw new TemplateError(path, source, cause.position, cause);
                  ^
      at Environment.compile (file:///Users/noel/Developer/projects/external/vento/src/environment.ts:144:17)
      at Environment.load (file:///Users/noel/Developer/projects/external/vento/src/environment.ts:208:29)
      at eventLoopTick (ext:core/01_core.js:175:7)
      at async file:///Users/noel/Developer/tests/vento-transformations/run.js:5:18
  Caused by: TransformError: [meriyah] [2:26-2:33]: Expected ')' while parsing compiled template function:
  
  2 __exports.content += (foo 'alpha', 'beta', 'gamma') ?? "";
                            ^
      at transformTemplateCode (file:///Users/noel/Developer/projects/external/vento/src/transformer.ts:150:11)
      at Environment.compile (file:///Users/noel/Developer/projects/external/vento/src/environment.ts:141:16)
      at Environment.load (file:///Users/noel/Developer/projects/external/vento/src/environment.ts:208:29)
      at eventLoopTick (ext:core/01_core.js:175:7)
      at async file:///Users/noel/Developer/tests/vento-transformations/run.js:5:18

• I added an argument to the Environment Function constructor to expose TemplateError class to the compiled template. I tried adding it to the Environment class (new this.error) but since TemplateError is hoisted it seemed cleaner to use it as a global.

• Moved errorLine to errors.ts and exported it so it can be used elsewhere. Not sure if you want errors.ts to be included as a module entrypoint.

Let me know if there's any corrections I can make! Thanks for taking a look.

[oscarotero]

Hi. Your changes look great!
I just left a question.

[noelforte]

Renamed VentoError to VentoBaseError (could also just be BaseError) which only overrides assignment of the error name so it doesn't need to be assigned explicitly. Because Error.constructor isn't overwritten, it can be reused on subclasses. As for calls to Error.captureStackTrace() you're correct that Error does this already; it was a lack of understanding on my part that I included it.

[oscarotero]

Great job! Thank you!