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.

.clang-tidy

@@ -1,5 +1,5 @@
 ---
-Checks: 'clang-diagnostic-*,clang-analyzer-*,-*,modernize-redundant-void-arg,modernize-use-bool-literals,modernize-use-default-member-init,modernize-use-nullptr,readability-braces-around-statements,readability-redundant-member-init'
+Checks: 'clang-diagnostic-*,clang-analyzer-*,-*,cppcoreguidelines-pro-type-member-init,modernize-redundant-void-arg,modernize-use-bool-literals,modernize-use-default-member-init,modernize-use-nullptr,readability-braces-around-statements,readability-redundant-member-init'
 WarningsAsErrors: ''
 HeaderFilterRegex: ''
 AnalyzeTemporaryDtors: false
@@ -13,6 +13,10 @@ CheckOptions:
     value:           '1'
   - key:             cppcoreguidelines-non-private-member-variables-in-classes.IgnoreClassesWithAllMemberVariablesBeingPublic
     value:           '1'
+  - key:             cppcoreguidelines-pro-type-member-init.IgnoreArrays
+    value:           '1'
+  - key:             cppcoreguidelines-pro-type-member-init.UseAssignment
+    value:           '1'
   - key:             google-readability-function-size.StatementThreshold
     value:           '800'
   - key:             google-readability-namespace-comments.ShortNamespaceLines