feat(@angular/cli): add support for multiple schematics collections - #22860

…s` to allow returning hidden schematics.

The return value of `listSchematicNames` will include hidden schematics when is invoked with true as first parameter.

By default, hidden schematics are not returned.

The `schematicCollections` can be placed under the `cli` option in the global `.angular.json` configuration, at the root or at project level in `angular.json` .

```jsonc
{
  "$schema": "./node_modules/@angular/cli/lib/config/schema.json",
  "version": 1,
  "cli": {
    "schematicCollections": ["@schematics/angular", "@angular/material"]
  }
  // ...
}
```

**Rationale**
When this option is not configured and a user would like to run a schematic which is not part of `@schematics/angular`,
the collection name needs to be provided to `ng generate` command in the form of `[collection-name:schematic-name]`. This make the `ng generate` command too verbose for repeated usages.

This is where `schematicCollections` comes handle. When adding `@angular/material` to the list of `schematicCollections`, the generate command will try to locate the schematic in the specified collections.

```
ng generate navigation
```

is equivalent to:

```
ng generate @angular/material:navigation
```

**Conflicting schematic names**
When multiple collections have a schematic with the same name. Both `ng generate` and `ng new` will run the first schematic matched based on the ordering (as specified) of `schematicCollections`.

DEPRECATED:

The `defaultCollection` workspace option has been deprecated in favor of `schematicCollections`.

Before
```json
"defaultCollection": "@angular/material"
```

After
```json
"schematicCollections": ["@angular/material"]
```

Closes #12157