[flutter_tools] use flutter tool handler for dwds resources and precache tool pub dependencies (#65814)

If the tool is downloaded from a precompiled snapshot, or if the backing source files in the pub cache are deleted, the dwds debugging functionality will break as the client.js file cannot be located. Instead use the PackageConfig to verify that package location, downloading if it is missing.

Override the dwds middleware to avoid Isolate.resolvePackageUri

Fixes #53644
Fixes #65475