Minor changs for Trailhead Module updates

Changes made:
* Moved `OpportunityInfo` out to a standalone class in order to allow it to be directly referenced by the `IOpportuntitesSelector` interface
* Updated the `IOpportuntitesSelector` interface to include all public methods which is standard practice.
* Minor tweaks to `OpportunitiesSelector` to improve readability.
* Added `Opportunity.Amount` to the query factory in the `OpportunitiesSelector.selectOpportunityInfo(Set<Id>)` method to fix Trailhead Issue TCF-022057

Author: ImJohnMDaniel

sfdx-source/apex-common-samplecode/main/classes/selectors/IOpportunitiesSelector.cls

@@ -26,5 +26,8 @@
 
 public interface IOpportunitiesSelector extends fflib_ISObjectSelector 
 {
+	List<Opportunity> selectById(Set<Id> idSet);
 	List<Opportunity> selectByIdWithProducts(Set<Id> idSet);
+	List<OpportunityInfo> selectOpportunityInfo(Set<Id> idSet);
+	Database.QueryLocator queryLocatorReadyToInvoice();
 }

sfdx-source/apex-common-samplecode/main/classes/selectors/OpportunitiesSelector.cls

@@ -82,34 +82,26 @@ public class OpportunitiesSelector extends fflib_SObjectSelector
 	public List<OpportunityInfo> selectOpportunityInfo(Set<Id> idSet)
 	{
 		List<OpportunityInfo> opportunityInfos = new List<OpportunityInfo>();
-		for(Opportunity opportunity : Database.query(
-				newQueryFactory(false).
-					selectField(opportunity.Id).
-					selectField(opportunity.StageName).
-					selectField('Account.Name').
-					selectField('Account.AccountNumber').
-					selectField('Account.Owner.Name').
-					setCondition('id in :idSet').
-					toSOQL()))
+
+		for(Opportunity opportunity : Database.query( newQueryFactory(false)
+														.selectField(Opportunity.Id)
+														.selectField(Opportunity.StageName)
+														.selectField(Opportunity.Amount)
+														.selectField('Account.Name')
+														.selectField('Account.AccountNumber')
+														.selectField('Account.Owner.Name')
+														.setCondition('id in :idSet')
+														.toSOQL() ))
+		{
 			opportunityInfos.add(new OpportunityInfo(opportunity));
+		}
+			
 		return opportunityInfos;	
 	}
 
 	public Database.QueryLocator queryLocatorReadyToInvoice()
 	{
 		return Database.getQueryLocator(
-			newQueryFactory().setCondition('InvoicedStatus__c = \'\'Ready\'\'').toSOQL());
-	}
-	
-	public class OpportunityInfo
-	{		 
-		private Opportunity opportunity;
-		public Id Id { get { return opportunity.Id; } }		
-		public Decimal Amount { get { return opportunity.Amount; } }		
-		public String Stage { get { return opportunity.StageName; } }		
-		public String AccountName { get { return opportunity.Account.Name; } }		
-		public String AccountNumber { get { return opportunity.Account.AccountNumber; } }		
-		public String AccountOwner { get { return opportunity.Account.Owner.Name; } }
-		private OpportunityInfo(Opportunity opportunity) { this.opportunity = opportunity; }		 
+			newQueryFactory().setCondition(Opportunity.InvoicedStatus__c + ' = \'Ready\'').toSOQL());
 	}
 }

sfdx-source/apex-common-samplecode/main/classes/selectors/OpportunityInfo.cls

@@ -0,0 +1,17 @@
+public class OpportunityInfo
+{
+    private Opportunity opportunity;
+
+    public OpportunityInfo(Opportunity opportunity)
+    {
+        this.opportunity = opportunity;
+    }
+
+    public Id Id { get { return this.opportunity.Id; } }
+    public Decimal Amount { get { return this.opportunity.Amount; } }
+    public String Stage { get { return this.opportunity.StageName; } }
+    public String AccountName { get { return this.opportunity.Account.Name; } }
+    public String AccountNumber { get { return this.opportunity.Account.AccountNumber; } }
+    public String AccountOwner { get { return this.opportunity.Account.Owner.Name; } }
+
+}

sfdx-source/apex-common-samplecode/main/classes/selectors/OpportunityInfo.cls-meta.xml

@@ -0,0 +1,5 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<ApexClass xmlns="http://soap.sforce.com/2006/04/metadata">
+    <apiVersion>55.0</apiVersion>
+    <status>Active</status>
+</ApexClass>