Rework MDL enum constants values

[pranavktiwari]

fixes MDEV-39184

Problem:

MDL constants values of 0 assign some default values (MDL_INTENTION_EXCLUSIVE, BACKUP) before MDL_REQUEST_INIT(). That does not make sense if MDL_REQUEST_INIT() was not called. Please rework the values of 0 into (MDL_NOT_INITIALIZED, NOT_INITIALIZED). Described by these comments in the code:

Fix

1- Increment all values in enum_mdl_type by 1.
2- Add a 0 at the start of the incompatibility arrays so the enum indices continue to match their corresponding bitmasks.
3- Update the MDL_BIT macro from (1U << A) to (1U << ((A) - 1)) to account for the enum shift.

This ensures that uninitialized MDL constants are correctly handled while preserving existing bitmask mappings.

[CLAassistant]

All committers have signed the CLA.

[midenok]

Hi @pranavktiwari,

Thank you for the patch! Now I see that change for MDL_BIT has negative effect on performance which is unwanted. I'd better tell in the description that it is investigation task and should be evaluated for push. Nonetheless, if we rework enum_mdl_type into bitmask values we would not need MDL_BIT() at all. What other problems occur if we try that?

It seems that I cannot recognize the changes for the second part of the ticket (about enum_mdl_namespace). Is it feasible to do these changes? Can you try to do it on the minimal set of code, without plugins and minor storage engines?