Treat stackalloc like array creation.

standard/expressions.md

@@ -1305,7 +1305,6 @@
     | anonymous_method_expression
     | pointer_member_access     // unsafe code support
     | pointer_element_access    // unsafe code support
-    | stackalloc_expression
     ;
 ```
 
@@ -2158,8 +2157,8 @@
 A *null_conditional_invocation_expression* is syntactically either a *null_conditional_member_access* ([§12.8.8](expressions.md#1288-null-conditional-member-access)) or *null_conditional_element_access* ([§12.8.13](expressions.md#12813-null-conditional-element-access)) where the final *dependent_access* is an invocation expression ([§12.8.10](expressions.md#12810-invocation-expressions)).
 
 A *null_conditional_invocation_expression* occurs within the context of a *statement_expression* ([§13.7](statements.md#137-expression-statements)), *anonymous_function_body* ([§12.19.1](expressions.md#12191-general)), or *method_body* ([§15.6.1](classes.md#1561-general)).
 
 Unlike the syntactically equivalent *null_conditional_member_access* or *null_conditional_element_access*, a *null_conditional_invocation_expression* may be classified as nothing.
 
 ```ANTLR
 null_conditional_invocation_expression
@@ -2722,6 +2721,7 @@
       array_initializer?
     | 'new' array_type array_initializer
     | 'new' rank_specifier array_initializer
+    | stackalloc_expression
     ;
 ```
 
@@ -3266,7 +3266,7 @@
 - one of the following value types: `sbyte`, `byte`, `short`, `ushort`, `int`, `uint`, `long`, `ulong`, `char`, `float`, `double`, `decimal`, `bool,`; or
 - any enumeration type.
 
 ### 12.8.22 Stack allocation
 
 A stack allocation expression allocates a block of memory from the execution stack. The ***execution stack*** is an area of memory where local variables are stored. The execution stack is not part of the managed heap. The memory used for local variable storage is automatically recovered when the current function returns.