Fix escape characters inside strings

[RedCMD]

Fixes #17057

Before:

After:

I am very confused as what this comment means:
"comment": "this is faster than the next begin/end rule since sub-pattern will match till end-of-line and SQL files tend to have very long lines."
I did some testing and found begin/end rules to be no slower than match
if anything, match was slightly slower due to microsoft/vscode-textmate#167

For some reason double quote strings did not support escape characters what so ever
Does SQL support escape characters inside double quote strings??

`backtick \` string`
'single quote \' string'
"double quote \" string"

should also support the double char escape sequence?

`backtick `` string`
'single quote '' string'
"double quote "" string"

[ghost]

All CLA requirements met.

[Charles-Gagnon]

Thanks for looking into this!

T-SQL escapes quotes (both ' and ") by doubling them up. The backslash escape sequence isn't valid.

So these are valid strings

SELECT 'foo''bar' -> foo'bar (escaped single quote)
SELECT 'foo"bar' -> foo"bar (double quote in single-quoted string)
SELECT '''' -> ' (escaped single quote)
SELECT "foo""bar" -> foo"bar (escaped double quote)
SELECT "foo'bar" -> foo'bar (single quote in double-quoted string)
SELECT """" -> " (escaped double quote)

Not valid

SELECT 'foo\'bar'
SELECT "foo\"bar"

(Note that there's some trickiness around double quotes where you have to use SET QUOTED_IDENTIFIER OFF to use them, but for now just assuming both types of quotes are valid is fine)

[cheenamalhotra]

Closing PR due to inactivity, please feel free to re-open when you have time to address feedback.

[panchoruy]

Incorrect highlighting of escaped quotes is still an issue on the current SQL syntax highlighting that ships with VSCode.
If T-SQL is supposed to behave differently then you should just provide that as a different Language Mode - rather than incorrectly highlighting all SQL that's not T-SQL.

[deemoney-rupendra]

The issue still persists. Can you please re-open this?

[Charles-Gagnon]

See #17057 for more discussion on this