fix(hcl2cdk): Handle multi-line strings better

[mutahhir]

Related issue

Fixes https://github.com/orgs/hashicorp/projects/207/views/12?pane=issue&itemId=25824022

Description

This is a pretty hacky PR, and I'm not really comfortable with the solution. That being said, I think this does resolve our immediate woes around heredocs.

The problem is as such: By the time the heredoc string comes in for parsing by the expression parser, (I suspect) the hcl2json parser has already converted it into a quote containing newlines. Quote with newlines are not accepted within HCL and thus breaks our expression.

This PR tries to detect newlines within string literals and wraps them back into a heredoc literal, making the expression parseable. As you can see from the PRs, this requires a lot of tweaks to existing logic to ensure it works ok, and even then, I'm not 100% sure this will not be caught off guard on other situations.

Checklist

• I have updated the PR title to match CDKTF's style guide
• I have run the linter on my code locally
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation if applicable
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works if applicable
• New and existing unit tests pass locally with my changes

[github-actions]

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