Deprecate UIApplicationMain & NSApplicationMain (#212)

Fixes: rdar://105803968

Author: amartini51

Style.md

@@ -111,6 +111,21 @@ Spelled as two words, not closed up or hyphenated.
 
 See entry for *Swift*.
 
+## deprecation
+
+In the language reference,
+include a deprecation note at the start of a section
+that describes a deprecated feature.
+Use wording and markup like the following:
+
+```
+> Deprecated:
+> This attribute is deprecated;
+> use the <doc:Attributes#main> attribute instead.
+> In Swift 6,
+> using this attribute will be an error.
+```
+
 ## definite initialization
 
 Not “definitive initialization”.

TSPL.docc/ReferenceManual/Attributes.md

@@ -1122,8 +1122,14 @@ for a method marked with the `objc` attribute.
 
 ### NSApplicationMain
 
+> Deprecated:
+> This attribute is deprecated;
+> use the <doc:Attributes#main> attribute instead.
+> In Swift 6,
+> using this attribute will be an error.
+
 Apply this attribute to a class
-to indicate that it's the application delegate.
+to indicate that it's the app delegate.
 Using this attribute is equivalent to calling the
 `NSApplicationMain(_:_:)` function.
 
@@ -2342,8 +2348,14 @@ The imported module must be compiled with testing enabled.
 
 ### UIApplicationMain
 
+> Deprecated:
+> This attribute is deprecated;
+> use the <doc:Attributes#main> attribute instead.
+> In Swift 6,
+> using this attribute will be an error.
+
 Apply this attribute to a class
-to indicate that it's the application delegate.
+to indicate that it's the app delegate.
 Using this attribute is equivalent to calling the
 `UIApplicationMain` function and
 passing this class's name as the name of the delegate class.