Sensible default field precision for new fields

[alexbruy]

Description

Couple of UX fixes related to fields length and precision:

• don't pre-select default geometry type in the new SpatiaLite dialog (consistent with other new layer dialogs)
• field length and precision validators in the New Memory Layer dialog now respect native provider types
• sensible default field precision in the Add Field dialog (same as in Field Calculator, fixes Sensible default width and precision for real columns #16581)

[nyalldawson]

Unrelated Travis nonsense

[uclaros]

@nyalldawson @alexbruy I think the newmemorydialog stuff should be done just like in qgsaddattrdialog. Read the native types for the provider, then fill the ui accordingly.
That way if we want to add a new type tomorrow or correct a type we do it in one place ( in the provider ), and also it will be safer from mistakes like setting the mWidth for the decimal number to 30 but its validator to 20, like in this PR.

[elpaso]

@alexbruy this commit causes a regression: try to add a new field to a PG layer, leave the default smallint type and save commits:

Could not commit changes to layer value

Errors: SUCCESS: 1 attribute(s) added.
ERROR: field with index 6 is not the same!
Provider: postgres
Storage: PostgreSQL database with PostGIS extension
expected field: name=ooo type=int typeName=int2 len=-1 precision=3
retrieved field: name=ooo type=int typeName=int2 len=-1 precision=0

The field is actually created but you cannot leave the editing state.

[alexbruy]

@elpaso should be fixed by #37697