extensions CHANGE cleanup API of the schema compiler for extension plugins

Be more clear by what API of the schema compiler is available for the
extension plugins. While the compilation context is needed, we want to
keep its members hidden to be able to make future changes. Therefore,
there is only a (possibly extensible in a future) set of getter to
access the context's members to be read and updated by the plugins'
compilation callbacks. Another part of the API is a set of compilation
flags to modify the behavior of the internal schema compiler.
diff --git a/src/plugins_exts.h b/src/plugins_exts.h
index 9f820d3..ebeead8 100644
--- a/src/plugins_exts.h
+++ b/src/plugins_exts.h
@@ -19,9 +19,10 @@
 #include "tree_edit.h"
 #include "tree_schema.h"
 
+#include "plugins_exts_compile.h"
+
 struct ly_ctx;
 struct lyd_node;
-struct lysc_ctx;
 
 #ifdef __cplusplus
 extern "C" {
@@ -45,19 +46,6 @@
 #define LYEXT_VERSION_CHECK uint32_t lyext_api_version = LYEXT_API_VERSION;
 
 /**
- * @defgroup extensionscompile YANG Extensions - Compilation Helpers
- * @ingroup extensions
- * @brief Helper functions to compile (via lyext_clb_compile callback) statements inside the extension instance.
- *
- * NOTE: There is a lot of useful static functions in the tree_schema_compile.c which could be provided here. Since we don't want
- * to have a large API with functions which will be never used, we provide here just the functions which are evidently needed.
- * If you, as an extension plugin author, need to make some of the compile functions available, please contact libyang maintainers
- * via the GITHUB issue tracker.
- *
- * @{
- */
-
-/**
  * @brief Possible cardinalities of the YANG statements.
  *
  * Used in extensions plugins to define cardinalities of the extension instance substatements.
@@ -91,7 +79,11 @@
 };
 
 /**
- * @brief YANG printer context.
+ * @brief Compiled YANG printer context for use in ::lyext_clb_schema_printer callback implementation.
+ *
+ * The structure provides basic information how the compiled schema is supposed to be printed and where. In the most simple
+ * case, the provided context is just passed into ::lysc_print_extension_instance() function which handles printing the
+ * extension's substatements in the standard way.
  */
 struct lys_ypr_ctx {
     struct ly_out *out;              /**< output specification */
@@ -102,13 +94,6 @@
 };
 
 /**
- * @brief Compile substatements of an extension instance.
- * TODO
- * @return LY_ENOT if the extension is disabled and should be ignored.
- */
-LY_ERR lys_compile_extension_instance(struct lysc_ctx *ctx, const struct lysp_ext_instance *ext_p, struct lysc_ext_instance *ext);
-
-/**
  * @brief Print substatements of an extension instance
  *
  * Generic function to access YANG printer functions from the extension plugins (::lyext_clb_schema_printer).
@@ -130,16 +115,6 @@
 void lysc_extension_instance_substatements_free(struct ly_ctx *ctx, struct lysc_ext_substmt *substmts);
 
 /**
- * @brief Duplicate the compiled extension (definition) structure.
- * TODO should this be in API? currently required by nacm_compile()
- * Instead of duplicating memory, the reference counter in the @p orig is increased.
- *
- * @param[in] orig The extension structure to duplicate.
- * @return The duplicated structure to use.
- */
-struct lysc_ext *lysc_ext_dup(struct lysc_ext *orig);
-
-/**
  * @brief Get pointer to the storage of the specified substatement in the given extension instance.
  *
  * The function simplifies access into the ::lysc_ext_instance.substmts sized array.
@@ -159,18 +134,6 @@
         void **instance_p, enum ly_stmt_cardinality *cardinality_p);
 
 /**
- * @brief Update path in the compile context, which is used for logging where the compilation failed.
- *
- * @param[in] ctx Compile context with the path.
- * @param[in] parent_module Module of the current node's parent to check difference with the currently processed module (taken from @p ctx).
- * @param[in] name Name of the node to update path with. If NULL, the last segment is removed. If the format is `{keyword}`, the following
- * call updates the segment to the form `{keyword='name'}` (to remove this compound segment, 2 calls with NULL @p name must be used).
- */
-void lysc_update_path(struct lysc_ctx *ctx, struct lys_module *parent_module, const char *name);
-
-/** @} extensionscompile */
-
-/**
  * @brief Callback to compile extension from the lysp_ext_instance to the lysc_ext_instance. The later structure is generally prepared
  * and only the extension specific data are supposed to be added (if any).
  *