Allow array to be used as a function name again

[alamb]

Rationale

#429 accidentally introduced a regression that found while testing downstream in DataFusion : apache/datafusion#1956

In particular, sql parser used to parse queries like this:

SELECT array(c1, cast(c2 as varchar)) FROM test

As a call to a function named array. However, after #429 it generates a parser error: SQL(ParserError("Expected [, found: ("))',

Changes

1. Restore the behavior of parsing array(..) as a function call.
2. Tests for same

Note array[] is still parsed as an array expression.

More details here #429 (comment)

cc @monadbobo

[coveralls]

Pull Request Test Coverage Report for Build 1953124295

• 14 of 14 (100.0%) changed or added relevant lines in 2 files are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage decreased (-0.01%) to 90.449%

---

Files with Coverage Reduction	New Missed Lines	%
src/parser.rs	1	83.77%

Totals
Change from base Build 1952654180:	-0.01%
Covered Lines:	7273
Relevant Lines:	8041

---

💛 - Coveralls

[coveralls]

Pull Request Test Coverage Report for Build 1953121049

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

• 13 of 13 (100.0%) changed or added relevant lines in 2 files are covered.
• 20 unchanged lines in 2 files lost coverage.
• Overall coverage decreased (-0.01%) to 90.449%

---

Files with Coverage Reduction	New Missed Lines	%
src/parser.rs	1	83.77%
tests/sqlparser_common.rs	19	99.02%

Totals
Change from base Build 1952654180:	-0.01%
Covered Lines:	7273
Relevant Lines:	8041

---

💛 - Coveralls

[coveralls]

Pull Request Test Coverage Report for Build 1953094762

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

• 13 of 13 (100.0%) changed or added relevant lines in 2 files are covered.
• 155 unchanged lines in 3 files lost coverage.
• Overall coverage decreased (-0.01%) to 90.449%

---

Files with Coverage Reduction	New Missed Lines	%
src/parser.rs	1	83.77%
tests/sqlparser_common.rs	19	99.02%
src/ast/mod.rs	135	77.54%

Totals
Change from base Build 1952654180:	-0.01%
Covered Lines:	7273
Relevant Lines:	8041

---

💛 - Coveralls