Import mbedtls-3.6.0

Imports Mbed TLS 3.6.0 from https://github.com/Mbed-TLS/mbedtls.git
tags mbedtls-3.6.0, v3.6.0

Files that are not needed are removed:

cd lib/libmbedtls
rm -rf mbedtls
cp -R path/to/mbedtls-3.6.0/mbedtls .
cd mbedtls
rm CMakeLists.txt DartConfiguration.tcl Makefile
rm .gitignore .travis.yml .pylintrc .globalrc .mypy.ini BRANCHES.md
rm include/.gitignore include/CMakeLists.txt library/.gitignore
rm library/CMakeLists.txt library/Makefile
rm -r cmake
rm -rf .git .github doxygen configs programs scripts tests visualc
rm -rf 3rdparty ChangeLog.d docs pkgconfig .gitmodules .readthedocs.yaml
rm library/mps_*
cd ..
git add mbedtls

This time we leave library/psa_* present to enable TLS 1.3 features.

This is a complete overwrite of previous code so earlier changes in the
previous branch import/mbedtls-3.4.0 will be added on top of this commit.

Signed-off-by: Tom Van Eyck <tom.vaneyck@kuleuven.be>
Acked-by: Jens Wiklander <jens.wiklander@linaro.org>
diff --git a/lib/libmbedtls/mbedtls/library/base64_internal.h b/lib/libmbedtls/mbedtls/library/base64_internal.h
new file mode 100644
index 0000000..a09bd23
--- /dev/null
+++ b/lib/libmbedtls/mbedtls/library/base64_internal.h
@@ -0,0 +1,45 @@
+/**
+ * \file base64_internal.h
+ *
+ * \brief RFC 1521 base64 encoding/decoding: interfaces for invasive testing
+ */
+/*
+ *  Copyright The Mbed TLS Contributors
+ *  SPDX-License-Identifier: Apache-2.0 OR GPL-2.0-or-later
+ */
+
+#ifndef MBEDTLS_BASE64_INTERNAL
+#define MBEDTLS_BASE64_INTERNAL
+
+#include "common.h"
+
+#if defined(MBEDTLS_TEST_HOOKS)
+
+/** Given a value in the range 0..63, return the corresponding Base64 digit.
+ *
+ * The implementation assumes that letters are consecutive (e.g. ASCII
+ * but not EBCDIC).
+ *
+ * \param value     A value in the range 0..63.
+ *
+ * \return          A base64 digit converted from \p value.
+ */
+unsigned char mbedtls_ct_base64_enc_char(unsigned char value);
+
+/** Given a Base64 digit, return its value.
+ *
+ * If c is not a Base64 digit ('A'..'Z', 'a'..'z', '0'..'9', '+' or '/'),
+ * return -1.
+ *
+ * The implementation assumes that letters are consecutive (e.g. ASCII
+ * but not EBCDIC).
+ *
+ * \param c     A base64 digit.
+ *
+ * \return      The value of the base64 digit \p c.
+ */
+signed char mbedtls_ct_base64_dec_value(unsigned char c);
+
+#endif /* MBEDTLS_TEST_HOOKS */
+
+#endif /* MBEDTLS_BASE64_INTERNAL */