Support AQUMV exact-match for multi-table JOIN queries

[avamingli]

Add a new AQUMV code path that rewrites multi-table JOIN queries to scan materialized views when the query exactly matches the MV definition. This compares the saved raw parse tree against stored viewQuery from gp_matview_aux, bypassing the single-table AQUMV logic entirely.

This enables significant query acceleration for common analytical patterns: instead of repeatedly computing expensive multi-table joins at query time, the planner can directly read pre-computed results from the materialized view, turning O(N*M) join operations into a simple sequential scan.

For example, given:

  CREATE MATERIALIZED VIEW mv AS
    SELECT t1.a, t2.b FROM t1 JOIN t2 ON t1.a = t2.a;

  -- Before (GUC off): original join plan
  Gather Motion 3:1
    ->  Hash Join
          Hash Cond: (t1.a = t2.a)
          ->  Seq Scan on t1
          ->  Hash
                ->  Seq Scan on t2

  -- After (GUC on): rewritten to MV scan
  Gather Motion 3:1
    ->  Seq Scan on mv

Fixes #ISSUE_Number

What does this PR do?

Type of Change

• Bug fix (non-breaking change)
• New feature (non-breaking change)
• Breaking change (fix or feature with breaking changes)
• Documentation update

Breaking Changes

Test Plan

• Unit tests added/updated
• Integration tests added/updated
• Passed make installcheck
• Passed make -C src/test installcheck-cbdb-parallel

Impact

Performance:

User-facing changes:

Dependencies:

Checklist

• Followed contribution guide
• Added/updated documentation
• Reviewed code for security implications
• Requested review from cloudberry committers

Additional Context

CI Skip Instructions

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[avamingli]

This commit implements exact-match rewriting, step2 of Materialized views with JOINs when Answer Query? .
The next step is non-exact-match rewriting which is the hardest part and is on my TODO list.