Merge 'Fix quote escape in literals' from Vrishabh

Previously we were not escaping the quotes properly in stirng literals
as shown below. The PR fixes that
limbo output without this PR
```
limbo> select '''a';
''a
limbo>  explain select '''a';
addr  opcode             p1    p2    p3    p4             p5  comment
----  -----------------  ----  ----  ----  -------------  --  -------
0     Init               0     4     0                    0   Start at 4
1     String8            0     1     0     ''a            0   r[1]='''a'
2     ResultRow          1     1     0                    0   output=r[1]
3     Halt               0     0     0                    0
4     Transaction        0     0     0                    0
5     Goto               0     1     0                    0
```
sqlite3 output
```
sqlite> select '''a';
'a
sqlite> explain select '''a';
addr  opcode         p1    p2    p3    p4             p5  comment
----  -------------  ----  ----  ----  -------------  --  -------------
0     Init           0     4     0                    0
1     String8        0     1     0     'a             0
2     ResultRow      1     1     0                    0
3     Halt           0     0     0                    0
4     Goto           0     1     0                    0
```
limbo output with this PR
```
limbo> select '''a';
'a
limbo> explain select '''a';
addr  opcode             p1    p2    p3    p4             p5  comment
----  -----------------  ----  ----  ----  -------------  --  -------
0     Init               0     4     0                    0   Start at 4
1     String8            0     1     0     'a             0   r[1]=''a'
2     ResultRow          1     1     0                    0   output=r[1]
3     Halt               0     0     0                    0
4     Transaction        0     0     0                    0
5     Goto               0     1     0                    0
```

Closes #616

core/translate/expr.rs

@@ -1854,7 +1854,7 @@ pub fn translate_expr(
             }
             ast::Literal::String(s) => {
                 program.emit_insn(Insn::String8 {
-                    value: s[1..s.len() - 1].to_string(),
+                    value: sanitize_string(s),
                     dest: target_register,
                 });
                 Ok(target_register)
@@ -2074,3 +2074,9 @@ pub fn get_name(
         _ => fallback(),
     }
 }
+
+/// Sanitaizes a string literal by removing single quote at front and back
+/// and escaping double single quotes
+pub fn sanitize_string(input: &str) -> String {
+    input[1..input.len() - 1].replace("''", "'").to_string()
+}

testing/select.test

@@ -11,6 +11,10 @@ do_execsql_test select-const-2 {
   SELECT 2
 } {2}
 
+do_execsql_test select-text-escape-1 {
+  SELECT '''a'
+} {'a}
+
 do_execsql_test select-blob-empty {
   SELECT x'';
 } {}