refactor(ivy): correctly type class declarations in ngtsc/ngcc (#29209)

Previously, several `ngtsc` and `ngcc` APIs dealing with class
declaration nodes used inconsistent types. For example, some methods of
the `DecoratorHandler` interface expected a `ts.Declaration` argument,
but actual `DecoratorHandler` implementations specified a stricter
`ts.ClassDeclaration` type.

As a result, the stricter methods would operate under the incorrect
assumption that their arguments were of type `ts.ClassDeclaration`,
while the actual arguments might be of different types (e.g. `ngcc`
would call them with `ts.FunctionDeclaration` or
`ts.VariableDeclaration` arguments, when compiling ES5 code).

Additionally, since we need those class declarations to be referenced in
other parts of the program, `ngtsc`/`ngcc` had to either repeatedly
check for `ts.isIdentifier(node.name)` or assume there was a `name`
identifier and use `node.name!`. While this assumption happens to be
true in the current implementation, working around type-checking is
error-prone (e.g. the assumption might stop being true in the future).

This commit fixes this by introducing a new type to be used for such
class declarations (`ts.Declaration & {name: ts.Identifier}`) and using
it consistently throughput the code.

PR Close #29209

packages/compiler-cli/src/ngtsc/util/src/typescript.ts

@@ -60,6 +60,11 @@ export function isDeclaration(node: ts.Node): node is ts.Declaration {
       ts.isFunctionDeclaration(node) || ts.isVariableDeclaration(node);
 }
 
+export function isNamedClassDeclaration(node: ts.Node): node is ts.ClassDeclaration&
+    {name: ts.Identifier} {
+  return ts.isClassDeclaration(node) && (node.name !== undefined);
+}
+
 export function isExported(node: ts.Declaration): boolean {
   let topLevel: ts.Node = node;
   if (ts.isVariableDeclaration(node) && ts.isVariableDeclarationList(node.parent)) {