[stdlib] name your constants better

- computed properties have an ABI impact; a function is fine here

Author: glessard

stdlib/public/core/SmallString.swift

@@ -94,7 +94,7 @@ extension _SmallString {
   }
 
   @_alwaysEmitIntoClient @inline(__always)
-  internal static var contiguousCapacity: Int {
+  internal static func contiguousCapacity() -> Int {
 #if _pointerBitWidth(_32) && os(watchOS)
     return capacity &- 2
 #else

stdlib/public/core/StringUTF8View.swift

@@ -409,7 +409,7 @@ extension String.UTF8View {
   public var _span: Span<UTF8.CodeUnit>? {
     @lifetime(borrow self)
     borrowing get {
-      if _guts.isSmall, _guts.count > _SmallString.contiguousCapacity {
+      if _guts.isSmall, _guts.count > _SmallString.contiguousCapacity() {
         return nil
       }
       return _underlyingSpan()

stdlib/public/core/Substring.swift

@@ -871,7 +871,8 @@ extension Substring.UTF8View {
   public var _span: Span<UTF8.CodeUnit>? {
     @lifetime(borrow self)
     borrowing get {
-      if _wholeGuts.isSmall, _wholeGuts.count > _SmallString.contiguousCapacity {
+      if _wholeGuts.isSmall,
+         _wholeGuts.count > _SmallString.contiguousCapacity() {
         // substring is spannable only when the whole string is spannable.
         return nil
       }

stdlib/public/core/UTF8Span.swift

@@ -291,7 +291,7 @@ extension String {
   public var _utf8Span: UTF8Span? {
     @lifetime(borrow self)
     borrowing get {
-      if _guts.isSmall, _guts.count > _SmallString.contiguousCapacity {
+      if _guts.isSmall, _guts.count > _SmallString.contiguousCapacity() {
         return nil
       }
       return unsafe UTF8Span(
@@ -426,7 +426,8 @@ extension Substring {
   public var _utf8Span: UTF8Span? {
     @lifetime(borrow self)
     borrowing get {
-      if _wholeGuts.isSmall, _wholeGuts.count > _SmallString.contiguousCapacity {
+      if _wholeGuts.isSmall,
+         _wholeGuts.count > _SmallString.contiguousCapacity() {
         // substring is spannable only when the whole string is spannable.
         return nil
       }