This commit adds support for templateUrl in component templates within
ngtsc. The compilation pipeline is split into sync and async versions,
where asynchronous compilation invokes a special preanalyze() phase of
analysis. The preanalyze() phase can optionally return a Promise which
will delay compilation until it resolves.
A ResourceLoader interface is used to resolve templateUrls to template
strings and can return results either synchronously or asynchronously.
During sync compilation it is an error if the ResourceLoader returns a
Promise.
Two ResourceLoader implementations are provided. One uses 'fs' to read
resources directly from disk and is chosen if the CompilerHost doesn't
provide a readResource method. The other wraps the readResource method
from CompilerHost if it's provided.
PR Close#24704
0c3738a780