fix: forbidden override between generic function and concrete generic function

[Changqing-JING]

Fixes #3013 .

Changes proposed in this pull request:
In current assemblyscript,

1. when concrete generic function override generic function
   Compile crashed

let called: string = "";

class A {
  foo<T>(x: T): void {
    called = "A";
  }
}

class B extends A {
  foo(x: i32): void {
    called = "B";
  }
}

let a: A = new B();
a.foo<i32>(1);
assert(called == "B");

Error message

node ./bin/asc.js --debug -o build/test.wasm -t build/test.wat test.ts
2
Debugger attached.

▌ Whoops, the AssemblyScript compiler has crashed during compile :-(
▌ 
▌ Here is the stack trace hinting at the problem, perhaps it's useful?
▌ 
▌ AssertionError: assertion failed
▌     at assert2 (/Users/Q479807/workspace/github/assemblyscript/std/portable/index.js:216:11)
▌     at Resolver.resolveFunction (/Users/Q479807/workspace/github/assemblyscript/src/resolver.ts:2790:7)
▌     at Resolver.resolveOverrides (/Users/Q479807/workspace/github/assemblyscript/src/resolver.ts:3077:39)
▌     at _Compiler.compile (/Users/Q479807/workspace/github/assemblyscript/src/compiler.ts:615:42)
▌     at Module.compile (/Users/Q479807/workspace/github/assemblyscript/src/index-wasm.ts:358:32)
▌     at Module.main (/Users/Q479807/workspace/github/assemblyscript/cli/index.js:732:31)
▌     at async file:///Users/Q479807/workspace/github/assemblyscript/bin/asc.js:33:22
▌ 
▌ If you see where the error is, feel free to send us a pull request. If not,
▌ please let us know: https://github.com/AssemblyScript/assemblyscript/issues
▌ 
▌ Thank you!

2. When generic function override concrete generic function
   The output is different with typescript.
   In typescript the output is B
   But in assemblyscript, the output is A

type i32 = number;
let trace = console.log;
class A {
  foo(x: i32): void {
    trace("A");
  }
}

class B extends A {
  foo<T>(x: T): void {
    trace("B");
  }
}

let a:A = new B();
a.foo(1);

Proposed solution

Assemblyscript can't follow typescript's behavior when override between generic and concrete generic function. Because typescript uses structural typing for type checking and erase type for code emitting.
But assemblyscript use nominal typing and need the type for code emitting. For example, in case 2, if assemblyscript need to follow typescript's behavior, it need a complex typing inference system to emit function B::foo. I don't think it's worth the effort

So this PR just totally forbidden override between generic function and concrete generic function

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