feat: EXPOSED-459 Open AbstractQuery.copyTo() to allow custom Query class extension

[bog-walk]

Description

Summary of the change:
Allows implementation of custom Query classes that do not lose stored properties of the original query. This may be useful for users that need niched or very database-specific clauses, for example MySQL query index hints.

Detailed description:

• Why:
  While it is possible to customize extension functions on the Query class, built-in class properties with private setters will not be copied to the new query instance when chaining/query building. The only properties copied would be those stored in base AbstractQuery. So these custom functions could not be used with original queries:

val originalQuery = TestTable.selectAll().where { TestTable.id eq 2 }.groupBy(TestTable.amount)

// when executed, there will be a WHERE clause (it is provided to Query constructor) but no GROUP BY clause
originalQuery
    .myCustomClause()
    .limit(1)
    .toList()

• What:
  This PR makes it possible to copy over all stored properties (not passed as an argument to the constructor) whenever a query instance is created or copied.
• How:
  The visibility modifier of AbstractQuery.copyTo() was made open and overriden in the Query class.

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Type of Change

Please mark the relevant options with an "X":

• New feature
• Documentation update

Affected databases:

• All

Checklist

• Unit tests are in place
• The build is green (including the Detekt check)
• All public methods affected by my PR has up to date API docs
• Documentation for my change is up to date

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Related Issues

EXPOSED-459