[ES|QL] Escape backslashes last (#205680)

## Summary

Closes elastic/kibana-team#1365
https://github.com/elastic/kibana/security/code-scanning/500

Moves backslash un-escaping last, after rall other un-escaping.


### Checklist

Check the PR satisfies following conditions. 

Reviewers should verify this PR satisfies this list as well.

- [ ] Any text added follows [EUI's writing
guidelines](https://elastic.github.io/eui/#/guidelines/writing), uses
sentence case text and includes [i18n
support](https://github.com/elastic/kibana/blob/main/src/platform/packages/shared/kbn-i18n/README.md)
- [ ]
[Documentation](https://www.elastic.co/guide/en/kibana/master/development-documentation.html)
was added for features that require explanation or tutorials
- [ ] [Unit or functional
tests](https://www.elastic.co/guide/en/kibana/master/development-tests.html)
were updated or added to match the most common scenarios
- [ ] If a plugin configuration key changed, check if it needs to be
allowlisted in the cloud and added to the [docker
list](https://github.com/elastic/kibana/blob/main/src/dev/build/tasks/os_packages/docker_generator/resources/base/bin/kibana-docker)
- [ ] This was checked for breaking HTTP API changes, and any breaking
changes have been approved by the breaking-change committee. The
`release_note:breaking` label should be applied in these situations.
- [ ] [Flaky Test
Runner](https://ci-stats.kibana.dev/trigger_flaky_test_runner/1) was
used on any tests changed
- [ ] The PR description includes the appropriate Release Notes section,
and the correct `release_note:*` label is applied per the
[guidelines](https://www.elastic.co/guide/en/kibana/master/contributing.html#kibana-release-notes-process)

### Identify risks

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to test bugs, performance regression, potential of data loss.

Describe the risk, its severity, and mitigation for each identified
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- [ ] [See some risk
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- [ ] ...

Author: vadimkibana

src/platform/packages/shared/kbn-esql-ast/src/parser/__tests__/literal.test.ts

@@ -116,6 +116,42 @@ describe('literal expression', () => {
           ],
         });
       });
+
+      it('escape double-quote before backslash', () => {
+        const text = `ROW "a\\"\\\\b", 1`;
+        const { root } = parse(text);
+
+        expect(root.commands[0]).toMatchObject({
+          type: 'command',
+          args: [
+            {
+              type: 'literal',
+              literalType: 'keyword',
+              name: '"a\\"\\\\b"',
+              valueUnquoted: 'a"\\b',
+            },
+            {},
+          ],
+        });
+      });
+
+      it('escape backslash before double-quote', () => {
+        const text = `ROW "a\\\\\\"b", 1`;
+        const { root } = parse(text);
+
+        expect(root.commands[0]).toMatchObject({
+          type: 'command',
+          args: [
+            {
+              type: 'literal',
+              literalType: 'keyword',
+              name: '"a\\\\\\"b"',
+              valueUnquoted: 'a\\"b',
+            },
+            {},
+          ],
+        });
+      });
     });
 
     describe('triple quoted', () => {

src/platform/packages/shared/kbn-esql-ast/src/parser/factories.ts

@@ -127,11 +127,11 @@ export function createLiteralString(ctx: StringContext): ESQLLiteral {
 
   if (!isTripleQuoted) {
     valueUnquoted = valueUnquoted
-      .replace(/\\\\/g, '\\')
       .replace(/\\"/g, '"')
       .replace(/\\r/g, '\r')
       .replace(/\\n/g, '\n')
-      .replace(/\\t/g, '\t');
+      .replace(/\\t/g, '\t')
+      .replace(/\\\\/g, '\\');
   }
 
   return Builder.expression.literal.string(