Move test files and baselines into subdirectories

Bug Report

VSCode can't really handle the number of files in the tests/cases/compiler directory (5386) or tests/baselines/reference (36655). It makes working with those directories very awkward!

There's plenty of scope for subdirectories, e.g.

anyAndUnknownHaveFalsyComponents.ts
anyAsReturnTypeForNewOnCall.ts
anyDeclare.ts
anyIdenticalToItself.ts
anyIndexedAccessArrayNoException.ts
anyInferenceAnonymousFunctions.ts
anyIsAssignableToObject.ts
anyIsAssignableToVoid.ts
anyMappedTypesError.ts
anyPlusAny1.ts
argsInScope.ts
arguments.ts
argumentsAsPropertyName.ts
argumentsAsPropertyName2.ts
argumentsBindsToFunctionScopeArgumentList.ts
argumentsObjectCreatesRestForJs.ts
argumentsObjectIterator01_ES5.ts
argumentsObjectIterator01_ES6.ts
argumentsObjectIterator02_ES5.ts
argumentsObjectIterator02_ES6.ts
argumentsObjectIterator03_ES5.ts
argumentsObjectIterator03_ES6.ts
argumentsReferenceInConstructor1_Js.ts
argumentsReferenceInConstructor2_Js.ts
argumentsReferenceInConstructor3_Js.ts
argumentsReferenceInConstructor4_Js.ts
argumentsReferenceInConstructor5_Js.ts
argumentsReferenceInConstructor6_Js.ts
argumentsReferenceInConstructor7_Js.ts
argumentsReferenceInMethod1_Js.ts
argumentsReferenceInMethod2_Js.ts
argumentsReferenceInMethod3_Js.ts
argumentsReferenceInMethod4_Js.ts
argumentsReferenceInMethod5_Js.ts
argumentsReferenceInMethod6_Js.ts
argumentsReferenceInMethod7_Js.ts
argumentsUsedInObjectLiteralProperty.ts
arithAssignTyping.ts
arithmeticOnInvalidTypes.ts
arithmeticOnInvalidTypes2.ts
arityErrorRelatedSpanBindingPattern.ts
arrayAssignmentTest1.ts
arrayAssignmentTest2.ts
arrayAssignmentTest3.ts
arrayAssignmentTest4.ts
arrayAssignmentTest5.ts
arrayAssignmentTest6.ts

Could be in these subdirectories

any
arguments
arithmetic
arity
arrayAssignment

I think that would cut down the number of subdirectories to something like 1000 which is much more reasonable. It could be a mostly automated change since the tests are named nicely and in most cases you could just group them by their first word (or maybe even first 1/2 letters?).

🔎 Search Terms

large number many files test cases baselines

Start by examining the layout and path assumptions around tests/cases/compiler and tests/baselines/reference, including how compiler tests locate their baselines. Group the test files and corresponding baselines into consistent subdirectories, then verify that the compiler test suite still discovers tests and matches every baseline after the move.