PHP 7.4 "trying to access..." errors

[boonebgorges]

See corresponding ticket and explanation in Core Trac: ​https://core.trac.wordpress.org/ticket/47704

We've got lots of these in BP.

[boonebgorges]

In 12598:

Fix PHP notice in BP_Activity_Activity test.

The $comments variable is already an array of ints, so wp_list_pluck() is
not needed. Changes in PHP 7.4 surface an error when used like this.

See #8264.

[boonebgorges]

In 12599:

Use shared fixtures in BP_Tests_XProfile_Activity.

Aside from improving speed, this allows us to skirt PHP 7.4 variable
access notices thrown when the fixtures were improperly created.

See #8264.

[boonebgorges]

In 12600:

Members: Don't attempt to remove member type terms when they don't match.

Attempting to use WP's taxonomy functions to remove non-existent terms
can trigger errors in PHP 7.4+.

See #8264.

[boonebgorges]

In 12601:

Groups: Don't attempt to remove group type terms when they don't match.

Attempting to use WP's taxonomy functions to remove non-existent terms
can trigger errors in PHP 7.4+.

See #8264.

[boonebgorges]

In 12602:

isset() checks for a variety of variable references.

This helps to avoid PHP notices in 7.4+.

See #8264.

[boonebgorges]

Tests are now passing locally on PHP 7.4, so I'm tentatively closing. Related commits can continue to reference this ticket.