Add support of EXPLAIN QUERY PLAN syntax for SQLite dialect

[git-hulk]

This closes #1455 and introduces one keyword: PLAN.

For the syntax documentation, please refer to:

https://sqlite.org/lang_explain.html

[coveralls]

Pull Request Test Coverage Report for Build 11227323789

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.

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Details

• 21 of 24 (87.5%) changed or added relevant lines in 3 files are covered.
• 297 unchanged lines in 5 files lost coverage.
• Overall coverage increased (+0.02%) to 89.326%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/parser/mod.rs	0	1	0.0%
tests/sqlparser_common.rs	18	20	90.0%

Files with Coverage Reduction	New Missed Lines	%
tests/sqlparser_snowflake.rs	1	98.01%
src/ast/mod.rs	2	82.47%
tests/sqlparser_sqlite.rs	5	98.15%
src/ast/ddl.rs	67	86.74%
src/parser/mod.rs	222	93.37%

Totals
Change from base Build 11186281805:	0.02%
Covered Lines:	30060
Relevant Lines:	33652

---

💛 - Coveralls

[git-hulk]

cc @iffyio

[iffyio]

can we skip the else condition if it works just as well to do?

if query_plan {
   write!()
}
if analyze {
  write!()
}

thinking that would keep this part simpler, even though the parser only accepts one or the other for the same statement

[git-hulk]

@iffyio Yes, that makes sense. It's better to keep the fmt simpler.

[iffyio]

LGTM! cc @alamb

[alamb]

Thanks @git-hulk and @iffyio