Show where mutated chilled strings were allocated

[etiennebarrie]

[Feature #20205]

The warning now suggests running with --debug-frozen-string-literal:

test.rb:3: warning: literal string will be frozen in the future (run with --debug-frozen-string-literal for more information)

When using --debug-frozen-string-literal, the location where the string was created is shown:

test.rb:3: warning: literal string will be frozen in the future
test.rb:1: the string was created here

When resurrecting strings and debug mode is not enabled, the overhead is a simple FL_TEST_RAW. When mutating chilled strings and deprecation warnings are not enabled, the overhead is a simple warning category enabled check.