cgen: reduce expense in repetitively called functions by using consts

[ttytm]

Those functions can be called quite often since the check nodes.

Using a constant declaration for the arrays with static data, instead of re-defining them per call, makes them a little cheaper.

🤖 Generated by Copilot at 0d659fa

Refactor C code generation for generic functions and methods in vlib/v/gen/c/fn.v by using a constant to escape generic brackets.

🤖 Generated by Copilot at 0d659fa

• Define a constant c_fn_name_escape_seq to hold the characters to be replaced in generic function names (link)
• Use c_fn_name_escape_seq instead of literal arrays to replace generic brackets in receiver and parameter type names of methods and functions (link, link)