Fix - Table question column type edge cases

[RomainLvr]

Checklist before requesting a review

Please delete options that are not relevant.

• I have performed a self-review of my code.
• I have added tests (when available) that prove my fix is effective or that my feature works.
• I have updated the CHANGELOG with a short functional description of the fix or new feature.
• This change requires a documentation update.

Description

• It fixes !43740
• Here is a brief description of what this PR does

Two related fixes for the Table question type's column configuration:

• Custom dropdown definitions (Setup > Dropdowns) all share one database table, distinguished only by a foreign key to their definition. Table columns using a custom dropdown as their type queried that table without filtering by definition, so every column showed the combined entries of all custom dropdown definitions instead of just its own. Fixed by scoping the query with the definition's own SQL criteria.
• The column-type dropdown offered question types (From Fields plugin) that need an extra "sub type" selector (e.g. a two-level picker) that Table's flat column-type list has no way to represent. Selecting one silently fell back to a plain text input with no indication anything was wrong. These types are now excluded from the list, using the same generic core mechanism (getSubTypes()) other plugins would use for this, no plugin-specific code added.
• Also remove new Reservation question type from available type cause of it's specific handling

[RomainLvr]

i'll send the patch to the customer for feedback

[stonebuzz]

The <select data-af-needs-ajax-s2> is rendered with zero <option> tags. If window.setupAjaxDropdown is unavailable at init time (script load failure, timing edge case), the user sees a native empty dropdown with no options and no placeholder text. A single disabled placeholder option would make the graceful-degradation state usable.

[stonebuzz]

The <select data-af-needs-ajax-s2> is rendered with zero <option> tags. If window.setupAjaxDropdown is unavailable at init time (script load failure, timing edge case), the user sees a native empty dropdown with no options and no placeholder text. A single disabled placeholder option would make the graceful-degradation state usable.