Add util function to remove trailing '\r'

Depending on the platform and adb versions, the lines output by adb
could end with "\r\r\n". This util function helps to remove all trailing
'\r'.

PR #2827 <https://github.com/Genymobile/scrcpy/pull/2827>

app/tests/test_str.c

@@ -384,6 +384,20 @@ static void test_index_of_column(void) {
     assert(sc_str_index_of_column("  a bc  d", 1, " ") == 2);
 }
 
+static void test_remove_trailing_cr() {
+    char s[] = "abc\r";
+    sc_str_remove_trailing_cr(s, sizeof(s) - 1);
+    assert(!strcmp(s, "abc"));
+
+    char s2[] = "def\r\r\r\r";
+    sc_str_remove_trailing_cr(s2, sizeof(s2) - 1);
+    assert(!strcmp(s2, "def"));
+
+    char s3[] = "adb\rdef\r";
+    sc_str_remove_trailing_cr(s3, sizeof(s3) - 1);
+    assert(!strcmp(s3, "adb\rdef"));
+}
+
 int main(int argc, char *argv[]) {
     (void) argc;
     (void) argv;
@@ -405,5 +419,6 @@ int main(int argc, char *argv[]) {
     test_wrap_lines();
     test_truncate();
     test_index_of_column();
+    test_remove_trailing_cr();
     return 0;
 }