fix(js_semantic): import namespace handling

[Conaclos]

Summary

Fix #2796

This PR improves the handling of import namespace in the JavaScript/TypeScript semantic model.

We now handle import namespace as TypeScript namespace: we consider them as values (variables) and allow their reference in an ambient context only inside a qualified name.
Some examples:

// Unused import
import * as Ns1 from "";
// This doesn't reference the import namespace `Ns1`
type T1 = Ns1; // Undeclared variable `Ns1`

namespace Ns2 {}
type T2 = Ns2; // Undeclared variable `Ns2`

import type * as Ns3 from "";
// `Ns3` references the import namespace because it is a qualified name.
type T3 = Ns3.Inner;

Unfortunately it is not enough because import namespace can be imported as a type.
In this specific case, we consider them as types.
However, it is always invalid of referencing a namespace in an unqualified name.
I added an exception in the name resolution where we report the reference as unresolved if it is not a qualified name and if it is referencing an import namespace.
This allows handling this case:

// Unused import
import type * as Ns from "";
]/ This doesn't reference the import namespace `Ns`
type T = Ns; // Undeclared variable `Ns`

I also fixed an issue where exporting as a type a TypeScript namespace was not correctly resolved.

namespace Ns {}
export type { Ns }; // This was previously reported as an undeclared type. It now refrences the namespace.

Test Plan

I added non-regression tests.

Mote: the new tests for useImportType and useExportType are not non-regression tests. More tests is always good no :)

[github-actions]

Parser conformance results on

js/262

Test result	main count	This PR count	Difference
Total	49701	49701	0
Passed	48721	48721	0
Failed	980	980	0
Panics	0	0	0
Coverage	98.03%	98.03%	0.00%

jsx/babel

Test result	main count	This PR count	Difference
Total	40	40	0
Passed	37	37	0
Failed	3	3	0
Panics	0	0	0
Coverage	92.50%	92.50%	0.00%

symbols/microsoft

Test result	main count	This PR count	Difference
Total	6322	6322	0
Passed	2036	2036	0
Failed	4286	4286	0
Panics	0	0	0
Coverage	32.20%	32.20%	0.00%

ts/babel

Test result	main count	This PR count	Difference
Total	662	662	0
Passed	593	593	0
Failed	69	69	0
Panics	0	0	0
Coverage	89.58%	89.58%	0.00%

ts/microsoft

Test result	main count	This PR count	Difference
Total	17646	17646	0
Passed	13439	13439	0
Failed	4205	4205	0
Panics	2	2	0
Coverage	76.16%	76.16%	0.00%