Support string module name and export * as

[JLHwung]

In this PR we implement the support of ES2022 string module names and ES2020 export * as ns. These two features are highly related so it end up in a single PR.

Summary

• AST changes: .quote is introduced to AST_SymbolImportForeign, AST_SymbolExportForeign and AST_SymbolExport. It will be " or ' if the module name is a string, otherwise it is undefined. I am not sure if we want to stick with the AST_Symbol prefix now that it can be a string, too. Anyway I will wait for more feedback before any drastic AST change
• Added new parser method as_symbol_or_string to handle export * as "f-oo"
• Added specific handling to differentiate between import { * as foo } and import { "*" as foo }

Limitation

The parser currently do not validate that module names should be a valid UTF16 string (no lone surrogate). It seems good to me since our parser is already a bit loose: cases like export { * as foo } from "x" will not throw.

Fixes #1137
Fixes #1231

[fabiosantoscode]

Excellent! I have no notes.

Not validating module names is fine, as you say. Terser doesn't validate a lot of things, because that's really not what it's built to do. It's garbage in, garbage out :)

I greatly appreciate this PR, thank you very much!