refactor(ast): remove JsImportNamespaceClause

[Conaclos]

Summary

While I was working on #428, I noticed that a namespace import, such as import * as X from "", can be represented in two ways. One way uses JsImportNamesapceClause and the other use JsNamespaceImportSpecifier embedded inside a JsNamedImportClause with a missing JsDefaultImportSpecifier.

This PR removes JsImportNamespaceClause and ensure that we have a unique way of representing a namespace import.

I think we should refactor the import AST nodes further. There is room for better factorization.

Test Plan

Updated snapshots.

[github-actions]

Parser conformance results on

js/262

Test result	main count	This PR count	Difference
Total	48863	48863	0
Passed	47808	47808	0
Failed	1055	1055	0
Panics	0	0	0
Coverage	97.84%	97.84%	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	6212	6212	0
Passed	1767	1767	0
Failed	4445	4445	0
Panics	0	0	0
Coverage	28.44%	28.44%	0.00%

ts/babel

Test result	main count	This PR count	Difference
Total	639	639	0
Passed	571	571	0
Failed	68	68	0
Panics	0	0	0
Coverage	89.36%	89.36%	0.00%

ts/microsoft

Test result	main count	This PR count	Difference
Total	17224	17224	0
Passed	13123	13123	0
Failed	4101	4101	0
Panics	0	0	0
Coverage	76.19%	76.19%	0.00%

[Conaclos]

I am closing this PR because I think my #436 is better