Use `woocommerce_valid_order_statuses_for_payment` in `pay_action` too

Even though it was possible to filter the statuses in my-order.php and other places,
it was not possible in the actual pay action.
Introduce `woocommerce_valid_order_statuses_for_payment_complete` filter

Since it's possible to filter the valid order statuses for payments and cancels,
it only makes sense to be able to do the same when checking which statuses
are valid for completing a payment.
Introduce `woocommerce_thankyou_order_received_text` filter
Supply order to thankyou text filter, if available
Update class-wc-admin-cpt-product.php

To handle bulk edit of "Sold Individually".
(The view part will follow in the next edit)
Update html-bulk-edit-product.php

The view part of "Sold Individually" bulk edit
Docblock fix: wc_product_post_type_link
Backorders at variation level

Added a new select metabox for variations allowing users to control
backorders at the variation level.
Might need more testing.
ref: #5351
Merge pull request #5308 from maxrice/master

Update REST API documentation link
Merge pull request #5317 from bassjobsen/patch-3

Update class-wc-frontend-scripts.php
Merge pull request #5321 from claudiosmweb/fix-quick-edit-duplicate-sku

Prevent duplicate sku when edit product using quick edit
Merge pull request #5327 from gedex/typo-fix

Typo fix.
Merge pull request #5325 from gedex/refactor_cpt-shop_order_custom_columns

Removes unused block and var.
Merge pull request #5326 from christian-thomas/patch-1

Update class-wc-emails.php
Merge pull request #5330 from splashingpixels/downloads-order-my-account

fixed my account downloadables out of order
Merge pull request #5331 from corsonr/settings-tooltip

fixed incorrect "order received" endpoint tooltip
Merge pull request #5319 from splashingpixels/passwords

removed wc_clean/sanitize_text_field not needed. handled by wp core func...
Merge pull request #5344 from tivnet/patch-3

Docblock fix: wc_product_post_type_link
Merge pull request #5342 from tivnet/patch-2

Update class-wc-admin-cpt-product.php
Clear cached API reports when deleting shop order transients