Optionally treat BRKs as two-byte instructions

Early data sheets listed BRK as one byte, but RTI after a BRK skips
the following byte, effectively making BRK a 2-byte instruction.
Sometimes, such as when diassembling Apple /// SOS code, it's handy
to treat it that way explicitly.

This change makes two-byte BRKs optional, controlled by a checkbox
in the project settings.  In the system definitions it defaults to
true for Apple ///, false for all others.

ACME doesn't allow BRK to have an arg, and cc65 only allows it for
65816 code (?), so it's emitted as a hex blob for those assemblers.
Anyone wishing to target those assemblers should stick to 1-byte mode.

Extension scripts have to switch between formatting one byte of
inline data and formatting an instruction with a one-byte operand.
A helper function has been added to the plugin Util class.

To get some regression test coverage, 2022-extension-scripts has
been configured to use two-byte BRK.

Also, added/corrected some SOS constants.

See also issue #44.

SourceGen/ProjectFile.cs

@@ -188,6 +188,7 @@ namespace SourceGen {
         public class SerProjectProperties {
             public string CpuName { get; set; }
             public bool IncludeUndocumentedInstr { get; set; }
+            public bool TwoByteBrk { get; set; }
             public int EntryFlags { get; set; }
             public string AutoLabelStyle { get; set; }
             public SerAnalysisParameters AnalysisParams { get; set; }
@@ -199,6 +200,7 @@ namespace SourceGen {
             public SerProjectProperties(ProjectProperties props) {
                 CpuName = Asm65.CpuDef.GetCpuNameFromType(props.CpuType);
                 IncludeUndocumentedInstr = props.IncludeUndocumentedInstr;
+                TwoByteBrk = props.TwoByteBrk;
                 EntryFlags = props.EntryFlags.AsInt;
                 AutoLabelStyle = props.AutoLabelStyle.ToString();
                 AnalysisParams = new SerAnalysisParameters(props.AnalysisParams);
@@ -495,6 +497,7 @@ namespace SourceGen {
             // Deserialize ProjectProperties: misc items.
             proj.ProjectProps.CpuType = Asm65.CpuDef.GetCpuTypeFromName(spf.ProjectProps.CpuName);
             proj.ProjectProps.IncludeUndocumentedInstr = spf.ProjectProps.IncludeUndocumentedInstr;
+            proj.ProjectProps.TwoByteBrk = spf.ProjectProps.TwoByteBrk;
             proj.ProjectProps.EntryFlags = Asm65.StatusFlags.FromInt(spf.ProjectProps.EntryFlags);
             if (Enum.TryParse<AutoLabel.Style>(spf.ProjectProps.AutoLabelStyle,
                     out AutoLabel.Style als)) {