Rename main to Main for Carbon style consistency (#939)

Main() is more consistency with Carbon's naming guidelines. C# offers some precedent: https://docs.microsoft.com/en-us/dotnet/csharp/fundamentals/program-structure/main-command-line

executable_semantics/testdata/function/auto_return/add.carbon

@@ -13,6 +13,6 @@ package ExecutableSemanticsTest api;
 
 fn add(x: i32, y: i32) -> auto { return x + y; }
 
-fn main() -> i32 {
+fn Main() -> i32 {
   return add(1, 2) - 3;
 }

executable_semantics/testdata/function/auto_return/fail_direct_recurse.carbon

@@ -20,6 +20,6 @@ fn Recurse(x: i32, do_recurse: Bool) -> auto {
   return x;
 }
 
-fn main() -> i32 {
+fn Main() -> i32 {
   return Recurse(1, true) - 3;
 }

executable_semantics/testdata/function/auto_return/fail_multiple_returns.carbon

@@ -21,6 +21,6 @@ fn Add(x: i32, y: i32) -> auto {
   }
 }
 
-fn main() -> i32 {
+fn Main() -> i32 {
   return Add(1, 2) - 3;
 }

executable_semantics/testdata/function/auto_return/fail_no_return.carbon

@@ -14,6 +14,6 @@ package ExecutableSemanticsTest api;
 fn NoReturn() -> auto {
 }
 
-fn main() {
+fn Main() {
   NoReturn();
 }

executable_semantics/testdata/function/auto_return/fail_separate_decl.carbon

@@ -16,6 +16,6 @@ fn Add(x: i32, y: i32) -> auto;
 
 fn Add(x: i32, y: i32) -> auto { return x + y; }
 
-fn main() -> i32 {
+fn Main() -> i32 {
   return Add(1, 2) - 3;
 }

executable_semantics/testdata/function/auto_return/modify_arg_type.carbon

@@ -19,6 +19,6 @@ fn f(x: Id(i32)) -> i32 {
   return x;
 }
 
-fn main() -> i32 {
+fn Main() -> i32 {
   return f(0);
 }

executable_semantics/testdata/function/auto_return/modify_return_type.carbon

@@ -15,6 +15,6 @@ fn Id(t: Type) -> auto { return t; }
 
 // Test non-trivial type expression in return type.
 
-fn main() -> Id(i32) {
+fn Main() -> Id(i32) {
   return 0;
 }

executable_semantics/testdata/function/auto_return/type.carbon

@@ -15,7 +15,7 @@ fn Id(t: Type) -> auto { return t; }
 
 // Test non-trivial type expression in variable declaration statement.
 
-fn main() -> i32 {
+fn Main() -> i32 {
   var x: Id(i32) = 0;
   return x;
 }

executable_semantics/testdata/function/empty_params.carbon

@@ -14,7 +14,7 @@ package ExecutableSemanticsTest api;
 // Test empty parameters and return type
 fn f() { }
 
-fn main() -> i32 {
+fn Main() -> i32 {
   f();
   return 0;
 }

executable_semantics/testdata/function/fail_call_with_tuple.carbon

@@ -13,7 +13,7 @@ package ExecutableSemanticsTest api;
 
 fn f(x: i32, y: i32) -> i32 { return x + y; }
 
-fn main() -> i32 {
+fn Main() -> i32 {
   var xy: (i32, i32) = (1, 2);
   // should fail to type-check
   return f(xy);

executable_semantics/testdata/function/fail_match_no_return.carbon

@@ -11,7 +11,7 @@
 
 package ExecutableSemanticsTest api;
 
-fn main() -> i32 {
+fn Main() -> i32 {
   var x: i32 = 0;
   match(0) {
     case 1 => { x = 1; }

executable_semantics/testdata/function/fail_match_partial_return.carbon

@@ -11,7 +11,7 @@
 
 package ExecutableSemanticsTest api;
 
-fn main() -> i32 {
+fn Main() -> i32 {
   var x: i32 = 0;
   match (0) {
     case 1 => { x = 1; }

executable_semantics/testdata/function/fail_non_exhaustive_match.carbon

@@ -11,7 +11,7 @@
 
 package ExecutableSemanticsTest api;
 
-fn main() -> i32 {
+fn Main() -> i32 {
   match (0) {
     case 1 => return 0;
   }

executable_semantics/testdata/function/fnty.carbon

@@ -15,7 +15,7 @@ fn add1(x: i32) -> i32 {
   return x + 1;
 }
 
-fn main() -> i32 {
+fn Main() -> i32 {
   var f: __Fn(i32)->i32 = add1;
   return f(-1);
 }

executable_semantics/testdata/function/ignored_parameter.carbon

@@ -15,6 +15,6 @@ fn ReturnSecond(_: i32, x: i32) -> i32 {
   return x;
 }
 
-fn main() -> i32 {
+fn Main() -> i32 {
   return ReturnSecond(1, 0);
 }

executable_semantics/testdata/function/multiple_args.carbon

@@ -16,6 +16,6 @@ fn f(x: i32, y: i32) -> i32 {
   return x + y;
 }
 
-fn main() -> i32 {
+fn Main() -> i32 {
   return f(2,3) - 5;
 }

executable_semantics/testdata/function/param_lifetime.carbon

@@ -19,7 +19,7 @@ fn f(x: i32) -> i32 {
   return 0;
 }
 
-fn main() -> i32 {
+fn Main() -> i32 {
   var a: i32 = 0; var b: i32 = 1;
   f(a);
   b = a;

executable_semantics/testdata/function/recursive.carbon

@@ -19,6 +19,6 @@ fn f(x: i32) -> i32 {
   }
 }
 
-fn main() -> i32 {
+fn Main() -> i32 {
   return f(2);
 }

executable_semantics/testdata/function/return.carbon

@@ -15,6 +15,6 @@ fn f(x: i32) -> i32 {
   return x - 1;
 }
 
-fn main() -> i32 {
+fn Main() -> i32 {
   return f(1);
 }

executable_semantics/testdata/function/return_exhaustive_match.carbon

@@ -11,7 +11,7 @@
 
 package ExecutableSemanticsTest api;
 
-fn main() -> i32 {
+fn Main() -> i32 {
   match (0) {
     case _: auto => return 1;
   }

executable_semantics/testdata/function/type_match.carbon

@@ -11,7 +11,7 @@
 
 package ExecutableSemanticsTest api;
 
-fn main() -> i32 {
+fn Main() -> i32 {
   var t: (auto, (i32, i32)) = ((1,2),(3,4));
   return t[0][0] + t[1][1] - 5;
 }