[refactor](parser) Dispatch parser statements by first token

[morrySnow]

What problem does this PR solve?

Issue Number: None

Related PR: None

Problem Summary: statementBase previously grouped unrelated statement families into one ANTLR adaptive prediction decision. This PR splits cross-prefix families and dispatches them through first-token-specific rules, changing generated statementBase() from one adaptivePredict call to a direct LA(1) switch. It also removes the redundant supported prefix from statement grammar rules and generated Context/visitor names; dispatcher rules use the *StatementDispatch suffix where the natural statement name is already occupied. All concrete grammar alternatives and FE behavior are preserved. Parent CST Context compatibility is intentionally out of scope because the standalone parser CST is not a public API.

Shared-host JMH rounds were rejected because they did not pass the predeclared noise gate, so this PR does not claim an unverified wall-clock improvement.

Release note

None

Check List (For Author)

• Test
  • Unit Test
    • ./run-fe-ut.sh --run org.apache.doris.sqlparser.StatementBaseDispatchTest,org.apache.doris.sqlparser.DorisSqlParserTest,org.apache.doris.nereids.parser.NereidsParserTest
    • 163 tests passed: 73 dispatch, 7 parser, and 83 Nereids parser/visitor tests.
  • Manual test
    • mvn checkstyle:check -pl fe-core
    • DISABLE_BUILD_UI=ON ./build.sh --fe
    • FE reactor BUILD SUCCESS with 0 Checkstyle violations.
• Behavior changed:
  • No.
• Does this need documentation?
  • No.

Check List (For Reviewer who merge this PR)

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

[hello-stephen]

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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?