feat(tax): adds getItemTaxLines (#6440)

**What**
- Selects the correct tax line for an item given a calculation context.

**For later PR**
- Consider optimizations. Some thoughts:
  - Even with global sales the number of rates in the DB is not likely to grow beyond ~1000.
  - Can large orders with hundreds of items optimize somehow?
  - Does it make sense to write a custom SQL query to do this?
- Support combined rate.

**Test cases covered**
The selection of tax rates take the following priority:

1. specific product rules - province
2. specific product type rules - province
3. default province rules
4. specific product rules - country
5. specific product type rules - country
6. default country rules

There are test cases for each of them under the following data seed structure:

### **US** 
- **Default Rate**: 2%
- **Sub-Regions**
  - CA 
    - Default Rate: 5%
    - Overrides
      - Reduced rate (for 3 product ids): 3%
      - Reduced rate (for product type): 1%
  - NY 
    - Default rate: 6%
  - FL 
    - Default rate: 4%
- **Overrides**
  - None

### **Denmark** 
- **Default rate:** 25% 
- **Sub-Regions**
  - None
- **Overrides**
  -  None

### **Germany** 
- **Default Rate:** 19%
- **Sub-Regions**
  - None
- **Overrides:**
  - Reduced Rate (for product type) - 7%

### **Canada** 
- **Default rate**: 5%
- **Sub-Regions**
  - QC 
    - Default rate: 2%
    - Overrides:
      - Reduced rate (for same product type as country reduced rate): 1%
  - BC 
    - Default rate: 2%
- **Overrides**
  - Reduced rate (for product id) - 3%
  - Reduced rate (for product type) - 3.5%

packages/tax/package.json

@@ -29,7 +29,7 @@
     "prepublishOnly": "cross-env NODE_ENV=production tsc --build && tsc-alias -p tsconfig.json",
     "build": "rimraf dist && tsc --build && tsc-alias -p tsconfig.json",
     "test": "jest --runInBand --bail --forceExit -- src/**/__tests__/**/*.ts",
-    "test:integration": "jest --runInBand --forceExit -- integration-tests/**/__tests__/**/*.ts",
+    "test:integration": "jest --runInBand --forceExit -- integration-tests/**/__tests__/**/*.spec.ts",
     "migration:generate": " MIKRO_ORM_CLI=./mikro-orm.config.dev.ts mikro-orm migration:generate",
     "migration:initial": " MIKRO_ORM_CLI=./mikro-orm.config.dev.ts mikro-orm migration:create --initial",
     "migration:create": " MIKRO_ORM_CLI=./mikro-orm.config.dev.ts mikro-orm migration:create",