[generator] Replace hyphens in managed names. - #498

Context: #464
Context: 7a309c4

Use of [Kotlin][0] can result in some "weird" method names and
parameter names in Java bytecode, in particular names which contain
spaces:

	// Kotlin
	abstract class Example {
	    public fun `method spaces`(`parameter spaces`: Double) {
	    }
	}

Run that through `kotlinc` and `javap`, and...there's a parameter
name with spaces!

	$ kotlinc -java-parameters hello.kt
	$ javap Example.class
	Classfile Example.class
	...
	public abstract class Example
	...
	  public final void method spaces(double);
	    ...
	    MethodParameters:
	      Name                           Flags
	      parameter spaces


...which is a sure fire way to confuse things.

Update `XmlApiImporter.EnsureValidIdentifier()` so that it uses
`IdentifierValidator.CreateValidIdentifier()` (7a309c4) to turn
potentially invalid strings such as `method spaces` into valid C#
identifiers such as `method_spaces`, which also ensures that method
names and constructor names are appropriately fixed.

Additionally, update `XmlApiImporter.CreateParameter()` so that it
now uses `EnsureValidIdentifier()`, ensuring it is consistent with
method and constructor name correction.

[0]: https://kotlinlang.org