[fix](json) Add . after in JSON path to support correct token parsing (#52543)

[mrhhsg]

Boost tokenizer requires explicit "." after "$" to correctly extract JSON path tokens. Without this, expressions like "$[0].key" cannot be properly split, causing issues in downstream logic. This commit ensures a "." is automatically added after "$" to maintain consistent token parsing behavior.

What problem does this PR solve?

Issue Number: close #xxx

Related PR: #52543

Problem Summary:

Release note

None

Check List (For Author)

• Test

  • Regression test
  • Unit Test
  • Manual test (add detailed scripts or steps below)
  • No need to test or manual test. Explain why:
    • This is a refactor/code format and no logic has been changed.
    • Previous test can cover this change.
    • No code files have been changed.
    • Other reason

• Behavior changed:

  • No.
  • Yes.

• Does this need documentation?

  • No.
  • Yes.

Check List (For Reviewer who merge this PR)

• Confirm the release note
• Confirm test cases
• Confirm document
• Add branch pick label

[Thearas]

Thank you for your contribution to Apache Doris.
Don't know what should be done next? See How to process your PR.

Please clearly describe your PR:

1. What problem was fixed (it's best to include specific error reporting information). How it was fixed.
2. Which behaviors were modified. What was the previous behavior, what is it now, why was it modified, and what possible impacts might there be.
3. What features were added. Why was this function added?
4. Which code was refactored and why was this part of the code refactored?
5. Which functions were optimized and what is the difference before and after the optimization?

[mrhhsg]

run buildall

[mrhhsg]

run buildall

[hello-stephen]

BE UT Coverage Report

Increment line coverage 28.57% (2/7) 🎉

Increment coverage report
Complete coverage report

Category	Coverage
Function Coverage	39.04% (10335/26470)
Line Coverage	30.03% (85836/285804)
Region Coverage	28.71% (44316/154357)
Branch Coverage	25.42% (22673/89184)

[mrhhsg]

run p0

[mrhhsg]

run buildall

[mrhhsg]

run p0

[mrhhsg]

run buildall

[doris-robot]

BE UT Coverage Report

Increment line coverage 10.71% (3/28) 🎉

Increment coverage report
Complete coverage report

Category	Coverage
Function Coverage	39.06% (10338/26470)
Line Coverage	30.04% (85836/285783)
Region Coverage	28.71% (44303/154334)
Branch Coverage	25.42% (22669/89168)

[mrhhsg]

run buildall

[hello-stephen]

BE UT Coverage Report

Increment line coverage 7.50% (3/40) 🎉

Increment coverage report
Complete coverage report

Category	Coverage
Function Coverage	39.05% (10338/26471)
Line Coverage	30.04% (85840/285795)
Region Coverage	28.70% (44293/154333)
Branch Coverage	25.42% (22667/89166)

[github-actions]

PR approved by at least one committer and no changes requested.

[github-actions]

PR approved by anyone and no changes requested.