BridgeJS: Escape reserved words in exported function parameters

[wfltaylor]

Currently parameter names using reserved words, such as extension or break, generate invalid Swift and/or JS. Reserved words are now escaped with backticks in Swift and with a leading underscore in JS. Originally I removed the parameter names from the generated thunks entirely, just using param0 param1 etc., but this made the generated code harder to read.

[krodak]

@JS func f(_ in: String) still generates invalid Swift and JS, because parseParameters (SwiftToSkeleton.swift:1590) keeps the backticks in param.name:

public func _bjs_f(_ `in`Bytes: Int32, _ `in`Length: Int32) -> Void {

f: function bjs_f(`in`) {
    const `in`Bytes = textEncoder.encode(`in`);

The import path already strips them with normalizeIdentifier. If this path does the same, the escaping in this PR covers both spellings:

let name = SwiftToSkeleton.normalizeIdentifier(param.secondName?.text ?? param.firstName.text)

@JS func checkEscaped(_ `in`: String) {}

[krodak]

For @JS protocol Delegate { func handle(in: Int) } the d.ts now has handle(_in: number), but the glue still uses in:

TestModule["bjs_Delegate_handle"] = function bjs_Delegate_handle(self, in) {

func handle(in: Int) -> Void {
    let inValue = in.bridgeJSLowerParameter()

@JSFunction func f(in: Int) has the same problem. It would be good to resolve in this PR, but follow up is fine as well ✌️ The JS side is in ImportedThunkBuilder.liftParameter:

} else if liftingFragment.parameters.count == 1 {
    let name = scope.variable(param.escapedJSIdentifier)
    parameterNames.append(name)
    valuesToLift = [name]
}

The Swift side needs backtickIfNeeded() where CallJSEmission.lowerParameter reads param.name.

[krodak]

This PR also changes the constructor and method paths. They generate correctly today, and these cases would keep it that way:

@JS class ReservedWordBox {
    @JS init(in: Int) {}
    @JS func run(for: Int) {}
    @JS static func make(default: Int) -> Int { 0 }
}