Normalize diagnostic messages

[msaraiva]

This PR brings a few important improvements when handling errors/warnings.

1. Format error message

Currently, the message is shown without any treatment. Example:

The most import part of the whole message is unexpected token: }. However, it's hard to spot it because there's too much pollution. To make it worse, if the path of the file is long enough, the message might be clipped or even completely hidden.

After this PR, it will look like this:

2. Properly handle errors in phoenix templates (eex and leex)

Currently, if an error occurs in a phoenix template, the editor points to the view file instead of the template. Example:

The following syntax error is not shown in the template:

But in the view, pointing to a line where there's no code:

After this PR, the editor points to the right file/line:

Additionally, this PR adds .eex and .leex files to the list of watched files by the server so that any changes in those files trigger recompilation.

3. Find the line in the stacktrace if the diagnostic does not provide it

When using macros, is common the see errors reported without the line. Example:

After this PR, the editor points to the write file/line if the line is available in the stacktrace:

[axelson]

Thanks for this! It looks like a great change. I'm going to test it locally for a bit to see if I run into any issues.

[axelson]

This looks great! It'll be a significant improvement to usability. ❤️