skip trying to substitute macros into lines that do not contain them

Currently, we try to substitute all macros into all lines by calling `subn` on the compiled regex, which results in an unmodified line if the line did not contain the macro at all. This call to `subn` is still quite expensive (runtime-wise).

To spare the cost, we now first check whether the line actually contains the macro text and skip the substitution check otherwise.
Please note that a line containing the macro text does not necessarily mean that a substitution will take place, since the simple containment is less strict than the regex (which checks that the macro is an actual token separated from the sounding context, as in `FOO` being in `FOO_BAR` but it should not be substituted).

Author: albertziegenhagel

fortls/parse_fortran.py

@@ -2234,6 +2234,10 @@ def replace_vars(line: str):
 
         # Substitute (if any) read in preprocessor macros
         for def_tmp, value in defs_tmp.items():
+            # Skip if the line does not contain the macro at all. This is supposed to
+            # spare the expensive regex-substitution in case we do not need it at all
+            if def_tmp not in line:
+                continue
             def_regex = def_regexes.get(def_tmp)
             if def_regex is None:
                 def_regex = re.compile(rf"\b{def_tmp}\b")