Fix syntax error when delimited column alias is used without preceding whitespace

[Anikait143]

Description

1. Issue

When the alias is directly adjacent to a keyword (like END) or a non-delimited column name, the error message mentions AS, even though there is no AS keyword in the query.

2. Changes made to fix the issue

• This bug is caused by ANTLR rewriting, we have added an extra space before 'AS' keyword when rewriting the query which which doesn't explicitly has 'AS' keyword before alias.

# Input
SELECT CASE WHEN 1=1  THEN 1 ELSE 0 END[c]

# previous output (wrong output)               
Msg 33557097, Level 16, State 1, Server persist-rcv-07mar-16-2-0-9, Line 1
syntax error at or near "ENDAS"

# current output (correct output)
~~START~~
int
1
~~END~~

# previous output (wrong output)
SELECT 1c;

Msg 33557097, Level 16, State 1, Server persist-rcv-07mar-16-2-0-9, Line 1
trailing junk after numeric literal at or near "1A"

# current output (correct output)
SELECT 1c;

~~START~~
int
1
~~END~~

• Added Test Cases for this issue

4_X PR: #2504

Task: BABEL-4863
Authored-by: Anikait Agrawal [email protected]
Signed-off-by: Anikait Agrawal [email protected]

Test Scenarios Covered

• Use case based - BABEL-4863-vu-*

• Boundary conditions -

• Arbitrary inputs -

• Negative test cases -

• Minor version upgrade tests -

• Major version upgrade tests -

• Performance tests -

• Tooling impact -

• Memory tests -

• Client tests -

Check List

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[jsudrik]

Approved based on the other reviews.