[mono][wasm] Refactor mono_fixup_symbol_name

[mkhamoyan]

This PR is a follow up for #101106

• Refactor mono_fixup_symbol_name to handle properly leaking the memory
• Apply same logic for all platforms

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[lambdageek]

1. important Don't return the address of a stack-allocated temporary.
2. Avoid C standard string manipulation functions that don't take a buffer length (like strcpy). Consider using GString from eglib instead.
3. Remove some of the duplicated logic about which characters are copied, which ones replaced by _ and which ones are encoded in hex.

[akoeplinger]

One comment, LGTM otherwise