Replaces MockInvokeContext by ThisInvokeContext in tests (#20881)

* Replaces MockInvokeContext by ThisInvokeContext in BpfLoader, SystemInstructionProcessor, CLIs, ConfigProcessor, StakeProcessor and VoteProcessor.

* Finally, removes MockInvokeContext, MockComputeMeter and MockLogger.

* Adjusts assert_instruction_count test.

* Moves ThisInvokeContext to the program-runtime crate.

program-runtime/src/log_collector.rs

@@ -0,0 +1,58 @@
+use std::cell::RefCell;
+
+const LOG_MESSAGES_BYTES_LIMIT: usize = 10 * 1000;
+
+#[derive(Default)]
+struct LogCollectorInner {
+    messages: Vec<String>,
+    bytes_written: usize,
+    limit_warning: bool,
+}
+
+#[derive(Default)]
+pub struct LogCollector {
+    inner: RefCell<LogCollectorInner>,
+}
+
+impl LogCollector {
+    pub fn log(&self, message: &str) {
+        let mut inner = self.inner.borrow_mut();
+
+        if inner.bytes_written + message.len() >= LOG_MESSAGES_BYTES_LIMIT {
+            if !inner.limit_warning {
+                inner.limit_warning = true;
+                inner.messages.push(String::from("Log truncated"));
+            }
+        } else {
+            inner.bytes_written += message.len();
+            inner.messages.push(message.to_string());
+        }
+    }
+}
+
+impl From<LogCollector> for Vec<String> {
+    fn from(log_collector: LogCollector) -> Self {
+        log_collector.inner.into_inner().messages
+    }
+}
+
+#[cfg(test)]
+pub(crate) mod tests {
+    use super::*;
+
+    #[test]
+    fn test_log_messages_bytes_limit() {
+        let lc = LogCollector::default();
+
+        for _i in 0..LOG_MESSAGES_BYTES_LIMIT * 2 {
+            lc.log("x");
+        }
+
+        let logs: Vec<_> = lc.into();
+        assert_eq!(logs.len(), LOG_MESSAGES_BYTES_LIMIT);
+        for log in logs.iter().take(LOG_MESSAGES_BYTES_LIMIT - 1) {
+            assert_eq!(*log, "x".to_string());
+        }
+        assert_eq!(logs.last(), Some(&"Log truncated".to_string()));
+    }
+}