AsyncSequence and protocol conformance rethrows (#35224)

* Initial draft of async sequences

* Adjust AsyncSequence associated type requirements

* Add a draft implementation of AsyncSequence and associated functionality

* Correct merge damage and rename from GeneratorProtocol to AsyncIteratorProtocol

* Add AsyncSequence types to the cmake lists

* Add cancellation support

* [DRAFT] Implementation of protocol conformance rethrowing

* Account for ASTVerifier passes to ensure throwing and by conformance rethrowing verifies appropriately

* Remove commented out code

* OtherConstructorDeclRefExpr can also be a source of a rethrowing kind function

* Re-order the checkApply logic to account for existing throwing calculations better

* Extract rethrowing calculation into smaller functions

* Allow for closures and protocol conformances to contribute to throwing

* Add unit tests for conformance based rethrowing

* Restrict rethrowing requirements to only protocols marked with @rethrows

* Correct logic for gating of `@rethrows` and adjust the determinates to be based upon throws and not rethrows spelling

* Attempt to unify the async sequence features together

* Reorder try await to latest syntax

* revert back to the inout diagnosis

* House mutations in local scope

* Revert "House mutations in local scope"

This reverts commit d91f1b25b59fff8e4be107c808895ff3f293b394.

* Adjust for inout diagnostics and fall back to original mutation strategy

* Convert async flag to source locations and add initial try support to for await in syntax

* Fix case typo of MinMax.swift

* Adjust rethrowing tests to account for changes associated with @rethrows

* Allow parsing and diagnostics associated with try applied to for await in syntax

* Correct the code-completion for @rethrows

* Additional corrections for the code-completion for @rethrows this time for the last in the list

* Handle throwing cases of iteration of async sequences

* restore building XCTest

* First wave of feedback fixes

* Rework constraints checking for async sequence for-try-await-in checking

* Allow testing of for-await-in parsing and silgen testing and add unit tests for both

* Remove async sequence operators for now

* Back out cancellation of AsyncIteratorProtocols

* Restructure protocol conformance throws checking and cache results

* remove some stray whitespaces

* Correct some merge damage

* Ensure the throwing determinate for applying for-await-in always has a valid value and adjust the for-await-in silgen test to reflect the cancel changes

* Squelch the python linter for line length

utils/gyb_syntax_support/StmtNodes.py

@@ -74,7 +74,8 @@ STMT_NODES = [
              Child('GuardResult', kind='Expr'),
          ]),
 
-    # for-in-stmt -> label? ':'? 'for' 'case'? pattern 'in' expr 'where'?
+    # for-in-stmt -> label? ':'? 
+    #   'for' 'try'? 'await'? 'case'? pattern 'in' expr 'where'?
     #   expr code-block ';'?
     Node('ForInStmt', kind='Stmt',
          traits=['WithCodeBlock', 'Labeled'],
@@ -84,6 +85,11 @@ STMT_NODES = [
              Child('LabelColon', kind='ColonToken',
                    is_optional=True),
              Child('ForKeyword', kind='ForToken'),
+             Child('TryKeyword', kind='TryToken', 
+                   is_optional=True),
+             Child('AwaitKeyword', kind='IdentifierToken',
+                   classification='Keyword',
+                   text_choices=['await'], is_optional=True),
              Child('CaseKeyword', kind='CaseToken',
                    is_optional=True),
              Child('Pattern', kind='Pattern'),