Fix TLetCorrection corrupting files with interior heredocs

[dduugg]

Problem

TLetCorrection (shared by Sorbet/RedundantTLet and Sorbet/RedundantTLetForLiteral) corrupts files when the T.let value contains an interior heredoc — one that is followed by more of the value's own source.

The mixin was written for heredocs at the tail of the value, where value_node.source stops at the marker and the body must be reattached. But when a heredoc sits in the interior of a larger value (e.g. a constructor call that continues after the heredoc), value_node.source already contains the heredoc body inline, so reattaching it duplicates the body.

Minimal repro:

PATH = T.let(
  Foo.new(
    a: <<~DIR,
      /usr/local
    DIR
    b: 2,
  ),
  Foo,
)

Autocorrect currently produces a duplicated, syntactically broken body:

PATH = Foo.new(
    a: <<~DIR,
      /usr/local
    DIR
    b: 2,
  )
      /usr/local   # <- duplicated
    DIR            # <- duplicated

Fix

Only reattach heredocs whose body/terminator extend past the value node's own source range (the tail heredocs). Interior heredocs already live inside value_node.source, so the plain corrector.replace(t_let_node, value_node.source) path handles them correctly.

Tests

Added test_offense_on_constant_constructor_with_interior_heredoc covering the case above. Full suite green (bundle exec rake test).

[KaanOzkan]

Nit: if heredocs.empty? reads funny. Can we either change the variable name (heredocs_to_reattach?) or add a comment to indicate these heredocs require special handling.