Add support for nested named/unnamed tuple types

[rhino1998]

This adds support for nested named and unnamed types with parameters like

    Tuple()
    Tuple(String, Int64)
    Tuple(String, Tuple(String, String))
    Tuple(a String, cd Tuple(c String, d String))

[coveralls]

Pull Request Test Coverage Report for Build 21455807828

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

• For more information on this, see Tracking coverage changes with pull request builds.
• To avoid this issue with future PRs, see these Recommended CI Configurations.
• For a quick fix, rebase this PR at GitHub. Your next report should be accurate.

Details

• 68 of 93 (73.12%) changed or added relevant lines in 1 file are covered.
• 790 unchanged lines in 2 files lost coverage.
• Overall coverage increased (+0.2%) to 51.521%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
parser/parser_column.go	68	93	73.12%

Files with Coverage Reduction	New Missed Lines	%
parser/parser_alter.go	54	72.97%
parser/ast.go	736	40.61%

Totals
Change from base Build 21280479720:	0.2%
Covered Lines:	8112
Relevant Lines:	15745

---

💛 - Coveralls

[git-hulk]

@rhino1998 Thanks for your contribution. Left two naming suggestions.

[git-hulk]

@rhino1998 Thank you!