Engine: Fix newline handling after heredoc terminators

[marcoroth]

This pull request fixes newline handling after heredoc terminators in ERB tags. When compiling an ERBContentNode containing a heredoc, the compiled Ruby could end up with syntactically invalid Ruby in two specific cases:

1. When the tag was at the start of a line, apply_trim appended " \n" (space + newline) as trailing whitespace after the code, which placed a trailing space on the heredoc terminator line. Ruby doesn't recognize a heredoc terminator with trailing whitespace characters.

   For the following snippet (from Engine: Herb builds invalid ruby when HEREDOC is present #1245):

   <%
     text = <<~TEXT
       Hello, world!
     TEXT
   %>

   The engine now produces:

   __herb = ::Herb::Engine; _buf = ::String.new; text = <<~TEXT
       Hello, world!
   -  TEXT 
   +  TEXT
   _buf.to_s

2. When the tag was not at the start of a line (inline), add_code appended ; instead of \n after the code, placing a semicolon directly after the heredoc terminator and thus altering the heredoc terminator.

   For the following snippet:

   <div><% text = <<~TEXT
       Hello, world!
     TEXT
   %></div>

   The engine now produces:

   __herb = ::Herb::Engine; _buf = ::String.new; _buf << '<div>'.freeze; text = <<~TEXT
       Hello, world!
   -  TEXT; _buf << '</div>
   +  TEXT
   + _buf << '</div>
    '.freeze;
    _buf.to_s

Related #1206
Resolves #1245

[pkg-pr-new]

npx https://pkg.pr.new/@herb-tools/formatter@1246

npx https://pkg.pr.new/@herb-tools/language-server@1246

npx https://pkg.pr.new/@herb-tools/linter@1246

commit: 39ff6a3

[github-actions]

🌿 Interactive Playground and Documentation Preview

A preview deployment has been built for this pull request. Try out the changes live in the interactive playground:

• Playground Preview
• Documentation Preview
• Website Preview

---

_{🌱 Grown from commit 39ff6a3}

---

✅ Preview deployment has been cleaned up.