fix(grammar): use fixed-length look-behind in FunC function definitions

The function-definition rule used a variable-length look-behind,
`(?<=^|[;{]\s*)`. Oniguruma accepts it, so VS Code highlighting is
unaffected, but engines that require fixed-length look-behind reject it
(for example the grammar compiler GitHub Linguist uses), which prevents
the grammar from being reused there.

Split the assertion into two fixed-length look-behinds, `(?<=^)` and
`(?<=[;{])`, and move `\s*` into the match. Behavior is unchanged: a
function name is still matched at the start of a line, or after `;` or `{`
with optional whitespace.

Author: 0xnirapod

editors/code/src/languages/syntaxes/func.tmLanguage.json

@@ -180,7 +180,7 @@
             "patterns": [
                 {
                     "name": "entity.name.function.definition.func",
-                    "match": "(?x)(?<=^|[;{]\\s*)(`[^`]+`|[A-Za-z_\\$][^\\s+\\-*\\/%,.;(){}\\[\\]=<>|\\^~]*)\\s*(?=\\()"
+                    "match": "(?x)(?:(?<=^)|(?<=[;{])\\s*)(`[^`]+`|[A-Za-z_\\$][^\\s+\\-*\\/%,.;(){}\\[\\]=<>|\\^~]*)\\s*(?=\\()"
                 },
                 {
                     "name": "variable.other.func",