Fix SetClipboardText for web

[ghost]

Issue cause

So, to the best of my knowledge and as deep as I could dig, the cause of the issue is as following:

1. text (L2145) has the correct string;
2. If text contains a \n, it will be passed exactly as \n to emscripten_run_script() (L2153);
3. So, instead of this:

str = "This is\na test."

4. It will end up like this (on the JS string):

str = "This is
a test."

5. And that will cause a SyntaxError: unterminated string literal (excellent example/demo here).
6. And, incidentally, confirms why using backticks template literals worked.

Proposed solution

After going through Emscripten's documentation (specially Calling JavaScript from C/C++ and Inline assembly/JavaScript), the best solution I could find was:

7. Replacing emscripten_run_script() by EM_ASM() (R2153) (doc);
8. And passing text to it with UTF8ToString() (R2153) (doc).

I believe this not only fixes the issue, but also improves the call because:

9. It's faster than emscripten_run_script() as the documentation mentions;
10. Gives us more control/flexibility over the JS syntax;
11. And, I think (please, correct me if I'm wrong) that it's also safer, because it doesn't use eval() like emscripten_run_script() (Mozilla documentation: eval() and Never use eval()!).

If there's any particular reason (specially security reasons) for not using EM_ASM() that I missed, please let me know.

Tested these proposed changes successfully on PLATFORM_WEB with Chromium (version 115.0.5790.170 64-bit) and Firefox (version 115.1.0esr 64-bit) both running on Linux (Linux Mint 21.1 64-bit).

Fixes #3251.

Edit 1: added line marks; editing.
Edit 2: added the test environment info.
Edit 3: added eval() documentation references.

[raysan5]

@ubkp Thank you very much for the issue investigation and detailed explanation! I think the proposed solution is the best one, I can't really see any downside at the moment.