Merge #20429: refactor: replace (sizeof(a)/sizeof(a[0])) with C++17 std::size

e829c9afbf refactor: replace sizeof(a)/sizeof(a[0]) by std::size (C++17) (Sebastian Falbesoner)
365539c846 refactor: init vectors via std::{begin,end} to avoid pointer arithmetic (Sebastian Falbesoner)
63d4ee1968 refactor: iterate arrays via C++11 range-based for loops if idx is not needed (Sebastian Falbesoner)

Pull request description:

  This refactoring PR picks up the idea of #19626 and replaces all occurences of `sizeof(x)/sizeof(x[0])` (or `sizeof(x)/sizeof(*x)`, respectively) with the now-available C++17 [`std::size`](https://en.cppreference.com/w/cpp/iterator/size)  (as [suggested by sipa](https://github.com/bitcoin/bitcoin/pull/19626#issuecomment-666487228)), making the macro `ARRAYLEN` obsolete.

  As preparation for this, two other changes are done to eliminate `sizeof(x)/sizeof(x[0])` usage:
  * all places where arrays are iterated via an index are changed to use C++11 range-based for loops If the index' only purpose is to access the array element (as [suggested by MarcoFalke](https://github.com/bitcoin/bitcoin/pull/19626#discussion_r463404541)).
  * `std::vector` initializations are done via `std::begin` and `std::end` rather than using pointer arithmetic to calculate the end (also [suggested by MarcoFalke](https://github.com/bitcoin/bitcoin/pull/20429#discussion_r567418821)).

ACKs for top commit:
  practicalswift:
    cr ACK e829c9afbf: patch looks correct
  fanquake:
    ACK e829c9afbf
  MarcoFalke:
    review ACK e829c9afbf 🌩

Tree-SHA512: b01d32c04b9e04d562b7717cae00a651ec9a718645047a90761be6959e0cc2adbd67494e058fe894641076711bb09c3b47a047d0275c736f0b2218e1ce0d193d

src/qt/networkstyle.cpp

@@ -22,7 +22,6 @@ static const struct {
     {"signet", QAPP_APP_NAME_SIGNET, 35, 15},
     {"regtest", QAPP_APP_NAME_REGTEST, 160, 30},
 };
-static const unsigned network_styles_count = sizeof(network_styles)/sizeof(*network_styles);
 
 // titleAddText needs to be const char* for tr()
 NetworkStyle::NetworkStyle(const QString &_appName, const int iconColorHueShift, const int iconColorSaturationReduction, const char *_titleAddText):
@@ -81,14 +80,12 @@ NetworkStyle::NetworkStyle(const QString &_appName, const int iconColorHueShift,
 const NetworkStyle* NetworkStyle::instantiate(const std::string& networkId)
 {
     std::string titleAddText = networkId == CBaseChainParams::MAIN ? "" : strprintf("[%s]", networkId);
-    for (unsigned x=0; x<network_styles_count; ++x)
-    {
-        if (networkId == network_styles[x].networkId)
-        {
+    for (const auto& network_style : network_styles) {
+        if (networkId == network_style.networkId) {
             return new NetworkStyle(
-                    network_styles[x].appName,
-                    network_styles[x].iconColorHueShift,
-                    network_styles[x].iconColorSaturationReduction,
+                    network_style.appName,
+                    network_style.iconColorHueShift,
+                    network_style.iconColorSaturationReduction,
                     titleAddText.c_str());
         }
     }

src/qt/platformstyle.cpp

@@ -23,7 +23,6 @@ static const struct {
     /* Other: linux, unix, ... */
     {"other", true, true, false}
 };
-static const unsigned platform_styles_count = sizeof(platform_styles)/sizeof(*platform_styles);
 
 namespace {
 /* Local functions for colorizing single-color images */
@@ -121,15 +120,13 @@ QIcon PlatformStyle::TextColorIcon(const QIcon& icon) const
 
 const PlatformStyle *PlatformStyle::instantiate(const QString &platformId)
 {
-    for (unsigned x=0; x<platform_styles_count; ++x)
-    {
-        if (platformId == platform_styles[x].platformId)
-        {
+    for (const auto& platform_style : platform_styles) {
+        if (platformId == platform_style.platformId) {
             return new PlatformStyle(
-                    platform_styles[x].platformId,
-                    platform_styles[x].imagesOnButtons,
-                    platform_styles[x].colorizeIcons,
-                    platform_styles[x].useExtraSpacing);
+                    platform_style.platformId,
+                    platform_style.imagesOnButtons,
+                    platform_style.colorizeIcons,
+                    platform_style.useExtraSpacing);
         }
     }
     return nullptr;