Add the ability for errors messages to link to error explanations

[mtoy-googly-moogly]

As mentioned in #1787 this adds the ability for an error message to contain a link to a longer error explanation.

• If an error messages ends with [xxx] then the xxx is extracted and added to the log entry as an error code
• Error message explanations will be added to https://docs.malloydata.dev/documentation/error_dictionary, since each section of the markdown file has a target, the target portion of the url is the "error code" which should be added to the message
• The VS Code extension is modified to display errors which contain a code, with a link to the error dictionary containing the target.

For example

        this.log(
          `pick type '${whenType}', expected '${returnType.dataType}'[pick-values-must-match]`
        );

## Pick values must match
The types of each `pick` (and the `else` if it is present), in a pick statement must match.
A message `type 'TYPENAME', expected 'TYPENAME'` indicates that the referenced source line
contains an expression whose type does not match the first `pick` in the pick statement. For example,
the following code would generate this error

   select: bad_pick is pick 1 when true else 'one'