Replace `absint( $meta_id)` check in `delete_metadata_by_mid`, etc

[peterwilsoncc]

Absint is run on the meta ID when deleting meta data, so calling delete_metadata_by_mid( 'user', -10 ) actually results in delete_metadata_by_mid( 'user', 10 ).

This is close but not close enough, instead the function can check it's a positive integer and fail if not.

Same applies to:

• update_metadata_by_mid
• get_metadata_by_mid

This will affect the related functions for particular meta types.

[peterwilsoncc]

In 37746.diff​:

• replace absint with intval
• return false if $meta_id is zero or lower.

[swissspidy]

Related: #37738, #33372.

[peterwilsoncc]

Milestoning this to join the related tickets mentioned above.

[peterwilsoncc]

In 37746.2.diff​:

• fail on negative numbers
• fail on floats
• get_metadata_by_mid( "1.0" ) is accepted

[peterwilsoncc]

In 38699:

Meta: Improve ID casting when getting, updating or deleting meta data.

Blindly casting IDs to absolute integers in get_metadata_by_mid(), update_metadata_by_mid() and delete_metadata_by_mid() can cause unexpected behaviour when a floating or negative number is passed.

Fixes #37746.