cmake: add CURL_GCC_ANALYZER option, enable in CI, fix/silence

Enable in one existing Linux, macOS and Windows job.

Cost:
- Linux: +1.3 minutes.
- macOS: +1.5 minutes.
- Windows: +2.5 minutes.

Fix or silence issues found:
- conncache: silence NULL deref warning.
  ```
  lib/conncache.c:564:18: warning: dereference of NULL '*data.multi' [CWE-476] [-Wanalyzer-null-dereference]
  ```
  Ref: ede6a8e087 #19378
- http2: check pointer for NULL.
  ```
  lib/http2.c:388:7: error: dereference of NULL ‘data’ [CWE-476] [-Wanalyzer-null-dereference]
  ```
- http2: silence potential NULL deref in `cf_h2_recv`.
  ```
  lib/http2.c: In function 'cf_h2_recv':
  lib/curl_trc.h:62:15: warning: dereference of NULL 'data' [CWE-476] [-Wanalyzer-null-dereference]
  ```
- openldap: silence deref before NULL check.
  Seen in GHA/Linux.
  ```
  lib/openldap.c: In function ‘oldap_state_mechs_resp’:
  lib/curl_trc.h:140:7: warning: check of ‘data’ for NULL after already dereferencing it [-Wanalyzer-deref-before-check]
  ```
- sendf: silence NULL deref false positive in `Curl_creader_set_fread`.
  It looks impossible to happen.
  ```
  lib/sendf.c:1133:7: warning: dereference of NULL 'r' [CWE-476] [-Wanalyzer-null-dereference]
  ```
- ws: silence deref before NULL check.
  ```
  lib/ws.c: In function 'ws_send_raw_blocking':
  lib/curl_trc.h:205:7: warning: check of 'data' for NULL after already dereferencing it [-Wanalyzer-deref-before-check]
  ```
- var: fix potential NULL deref
  ```
  src/var.c:216:29: warning: dereference of NULL 'envp' [CWE-476] [-Wanalyzer-null-dereference]
  ```
- cli_hx_upload.c: fix NULL check after dereference.
  ```
  tests/libtest/cli_hx_upload.c:170:7: warning: check of '*t.method' for NULL after already dereferencing it [-Wanalyzer-deref-before-check]
  ```
- unit1607, unit1609: fix theoretical NULL ptr dereference.
  ```
  tests/unit/unit1607.c:211:12: warning: dereference of NULL 'addr' [CWE-476] [-Wanalyzer-null-dereference]
  tests/unit/unit1609.c:193:12: warning: dereference of NULL 'addr' [CWE-476] [-Wanalyzer-null-dereference]
  ```
- globally disable checks triggering false positives only:
  ```
  docs/examples/externalsocket.c:135:8: warning: 'connect' on possibly invalid file descriptor 'sockfd' [-Wanalyzer-fd-use-without-check]
  lib/bufq.c:465:16: warning: infinite loop [CWE-835] [-Wanalyzer-infinite-loop] (gcc-15 Windows)
  lib/doh.c:1035:34: warning: stack-based buffer over-read [CWE-126] [-Wanalyzer-out-of-bounds] (gcc-15 macOS)
  lib/ftp.c:4022:20: warning: infinite loop [CWE-835] [-Wanalyzer-infinite-loop] (gcc-15 macOS)
  lib/http2.c:689:28: warning: buffer over-read [CWE-126] [-Wanalyzer-out-of-bounds] (gcc-15 macOS)
  lib/socketpair.c:195:5: warning: leak of file descriptor 'curl_dbg_socket(2, 1, 0, 192, "D:/a/curl/curl/lib/socketpair.c")' [CWE-775] [-Wanalyzer-fd-leak]
  src/tool_doswin.c:810:7: warning: leak of file descriptor '*tdata.socket_l' [CWE-775] [-Wanalyzer-fd-leak]
  src/tool_doswin.c:816:9: warning: leak of file descriptor '*tdata.socket_l' [CWE-775] [-Wanalyzer-fd-leak]
  src/tool_main.c:96:1: warning: leak of file descriptor 'fd[0]' [CWE-775] [-Wanalyzer-fd-leak]
  src/tool_main.c:96:1: warning: leak of file descriptor 'fd[1]' [CWE-775] [-Wanalyzer-fd-leak]
  src/tool_urlglob.c:48:17: warning: leak of 'malloc(8)' [CWE-401] [-Wanalyzer-malloc-leak]
  src/tool_writeout.c:870:3: warning: leak of FILE 'stream2' [CWE-775] [-Wanalyzer-file-leak]
  tests/libtest/lib518.c:90:1: warning: leak of FILE [CWE-775] [-Wanalyzer-file-leak]
  tests/libtest/lib537.c:87:1: warning: leak of FILE [CWE-775] [-Wanalyzer-file-leak]
  tests/server/tftpd.c:1147:10: warning: 'bind' on possibly invalid file descriptor 'sock' [-Wanalyzer-fd-use-without-check]
  tests/server/tftpd.c:1155:10: warning: 'bind' on possibly invalid file descriptor 'sock' [-Wanalyzer-fd-use-without-check]
  tests/server/tftpd.c:1259:10: warning: 'connect' on possibly invalid file descriptor '4294967295' [-Wanalyzer-fd-use-without-check]
  ```

Also:
- cmake: update clang-tidy typecheck comment.

Ref: https://gcc.gnu.org/onlinedocs/gcc/Static-Analyzer-Options.html

Closes #20921

lib/http2.c

@@ -375,6 +375,10 @@ static CURLcode http2_data_setup(struct Curl_cfilter *cf,
 
   (void)cf;
   DEBUGASSERT(data);
+
+  if(!data)
+    return CURLE_BAD_FUNCTION_ARGUMENT;
+
   stream = H2_STREAM_CTX(ctx, data);
   if(stream) {
     *pstream = stream;
@@ -1940,10 +1944,15 @@ static CURLcode cf_h2_recv(struct Curl_cfilter *cf, struct Curl_easy *data,
                            char *buf, size_t len, size_t *pnread)
 {
   struct cf_h2_ctx *ctx = cf->ctx;
-  struct h2_stream_ctx *stream = H2_STREAM_CTX(ctx, data);
+  struct h2_stream_ctx *stream;
   CURLcode result, r2;
   struct cf_call_data save;
 
+  if(!data)
+    return CURLE_HTTP2;
+
+  stream = H2_STREAM_CTX(ctx, data);
+
   *pnread = 0;
   if(!stream) {
     /* Abnormal call sequence: either this transfer has never opened a stream