Destructuring declaration prefers type annotation type (#25282)

* Destructuring declaration prefers type annotation type

Previously, getTypeForBindingElement would always union the declarations type and
the type of the default initializer. Now, if the declaration has a type
annotation, it does not union with the initializer type. The type
annotation's type is the one used.

* Small cleanup in parentDeclarationHasTypeAnnotation

* Refactoring based on PR comments

* Combine getCombined*Flags into a single helper function

Retain the individual functions since they are used a lot.

* Remove unneeded temp

tests/cases/conformance/es6/destructuring/destructuringParameterDeclaration8.ts

@@ -0,0 +1,18 @@
+// explicit type annotation should cause `method` to have type 'x' | 'y'
+// both inside and outside `test`.
+function test({
+    method = 'z',
+    nested: { p = 'c' }
+}: {
+    method?: 'x' | 'y',
+    nested?: { p: 'a' | 'b' }
+})
+{
+    method
+    p
+}
+
+test({});
+test({ method: 'x', nested: { p: 'a' } })
+test({ method: 'z', nested: { p: 'b' } })
+test({ method: 'one', nested: { p: 'a' } })