fix(parser): preserve process substitution contexts (#351)

* fix(parser): preserve process substitution contexts

* fix(parser): preserve heredoc delimiter literals

* fix(parser): preserve joined process body words

* fix(parser): preserve heredoc body expansion

* fix(parser): preserve adjacent word context

* fix(parser): preserve literal process boundaries

* refactor(parser): simplify process substitution parsing

* fix(parser): preserve recursive process syntax

* fix(parser): preserve process closing boundaries

* Revert "fix(parser): preserve process closing boundaries"

This reverts commit 967300dcf768003b72b9510e3e203126172f34e1.