Support backtick'ed function names

[lervag]

Kotlin has special syntax defined for Java interoperability where e.g. function names can be defined to be more or less anything delimited by backticks, e.g. (source: https://stackoverflow.com/a/65923081/51634):

fun `adding 3 and 4 should be equal to 7`() {
    assertEquals(calculator.add(3, 4), 7)
}

The documentation for this feature seems to be here:

• https://kotlinlang.org/docs/java-interop.html#escaping-for-java-identifiers-that-are-keywords-in-kotlin
• https://kotlinlang.org/docs/coding-conventions.html#names-for-test-methods

Notice that this feature is common for test functions. As such, I hope it could be possible to add support for it in the tree-sitter grammar.