HHH-19701 add 'if exists' to 'drop sequence' on Maria

[gavinking]

[Please describe here what your change is about]

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https://hibernate.atlassian.net/browse/HHH-19701

[WolfgangHG]

@gavinking I think this is not expected - your change adds "if exists" to the default "drop sequence" statement which applies to all databases (though they might not support it). My idea was to implement/override the method getDropSequenceString in https://github.com/hibernate/hibernate-orm/blob/main/hibernate-core/src/main/java/org/hibernate/dialect/sequence/MariaDBSequenceSupport.java

[gavinking]

Ouch, of course, that's totally what I meant to do.

Absolutely crazy that no tests failed.

I guess because most other dialects also override that method.

Anyway, #10744.