Escape `_` in LIKE to allow index search

Also filters for expired sessions in DB, not PHP.
Fixes #6916
Don't return option_value from cleanup_sessions() query, no longer required
woocommerce_price_filter_meta_keys filter to allow plugins to define min/max meta keys that require searching

Closes #6492
Leave postcode before city swapping to JS

Fixes #6842
Fix possible notice
Fix admin term output

Resolves an issue decoding foreign chars caused by #6555
Fixes #6550
Add special wc_query variable when querying products. #6444
Merge pull request #6920 from SiR-DanieL/patch-2

Fix possible notice with taxes
Merge pull request #6917 from webaware/cleanup-sessions-escape-for-like

Escape `_` in LIKE to allow index search
Clarify variable comment #6830
[2.2] remove_taxes needs to clear line_tax_data
[2.2] If order_item_type is not set, don't query it in reports class
coupons. closes #6836
shipping calculator. #6412
Allow plugins to filter the taxable location

Passes tax_class so we can workaround mixed carts and EU VAT.
cc @barrykooij