Simplify: Squash the MD5 & NormalizerValue & OptimizerHints mixins into the base dialect

[nolar]

Little improvements step by step:

Following the removal of unused mixins in #753, remove the last ones that are still used: OptimizerHints, MD5 & NormalizerValue.

Simply squash their methods into the base dialect class. The MD5 & Normalizer are present in ALL our databases, so there is no change required from the real dialect classes anyway.

The OptimizerHints mixin is present only in MS SQL, MySQL, and Oracle. But it was using the undeclared methods where called, so it was buggy anyway (if it was used at all). Now, we will add optimizer hints in all databases, though most of them will ignore this comment.

In the end, we get a plain & simple hierarchy of dialects: BaseDialect -> specific WhateverDialect — with no multiple inheritance and unclear source of methods.

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If that helps, here is the matrix of databases & their mixins that they inherit from:

NV AbstractMixin_NormalizeValue
MD AbstractMixin_MD5
SC AbstractMixin_Schema                 Many, but no default behaviour; UNUSED? except in 2 tests
RS AbstractMixin_RandomSample           Only DuckDB? no default behaviour; UNUSED?
TT AbstractMixin_TimeTravel             Only BigQUery & Snowflake, no default behaviour; UNUSED?
OH AbstractMixin_OptimizerHints         Only MS SQL, MySQL, Oracle, no default behaviour
rSC Mixin_Schema                        UNUSED!
rRS Mixin_RandomSample                  UNUSED!
rOH Mixin_OptimizerHints


Dialect👉   AbstractMixin_…   Mixin_…
Db👇        NV MD SC RS TT OH rSC rRS rOH

bigquery    +  +  +  -  +  -   -   -   -
clickhouse  +  +  -  -  -  -   -   -   -
databricks  +  +  -  -  -  -   -   -   -
duckdb      +  +  +  +  -  -   +   -   -
mssql       +  +  +  -  -  +   +   -   +
mysql       +  +  +  -  -  +   +   -   +
oracle      +  +  +  -  -  +   -   -   +
postgresql  +  +  +  -  -  -   +   -   -
presto      +  +  +  -  -  -   +   -   -
snowflake   +  +  +  -  +  -   -   -   -
vertica     +  +  +  -  -  -   -   -   -

redshift    +  +  +  -  -  -   +   -   -  == postgres
trino       +  +  +  -  -  -   +   -   -  == presto

ALL of them +  +  -  -  -  -   -   -!  -