Style: Partially apply clang-tidy's cppcoreguidelines-pro-type-member-init

Didn't commit all the changes where it wants to initialize a struct
with `{}`. Should be reviewed in a separate PR.

Option `IgnoreArrays` enabled for now to be conservative, can be
disabled to see if it proposes more useful changes.

Also fixed manually a handful of other missing initializations / moved
some from constructors.

platform/linuxbsd/detect_prime_x11.cpp

@@ -55,7 +55,7 @@
 typedef GLXContext (*GLXCREATECONTEXTATTRIBSARBPROC)(Display *, GLXFBConfig, GLXContext, Bool, const int *);
 
 struct vendor {
-	const char *glxvendor;
+	const char *glxvendor = nullptr;
 	int priority = 0;
 };