feat: Thai VAT schemes as Sales/Purchase Taxes and Charges Templates

Per Thai company: Thailand VAT 7%, Thailand VAT 7% (Included) for
VAT-inclusive pricing, Thailand VAT 0% for zero-rated supplies. Sales
schemes post to Output VAT, purchase schemes to Input VAT (category
Total, so recoverable VAT stays out of valuation). The 7% scheme is the
default when the company has none. Created on Company save, after
install, and by a patch for existing companies.

default_thai_company/tax_withholding.py

@@ -118,9 +118,14 @@ def prepare_fixture_accounts(doc, method=None):
 			link_company(doc, company, ensure_company_accounts(company))
 
 
+def company_ready(doc):
+	"""A Thai company whose chart of accounts exists."""
+	return doc.country == "Thailand" and frappe.db.exists("Account", {"company": doc.name})
+
+
 def setup_company(doc, method=None):
 	"""Company.on_update: create the tax accounts and link every WHT category."""
-	if doc.country != "Thailand" or not frappe.db.exists("Account", {"company": doc.name}):
+	if not company_ready(doc):
 		return
 
 	account = ensure_company_accounts(doc.name)