refactor: combine regexp files

regext_bt.c and regexp_nfa.c are inlined into regexp.c instead of
included as a header. This makes developer tools like clang-tidy and
clangd be able to understand the code better.

src/nvim/CMakeLists.txt

@@ -362,12 +362,6 @@ list(APPEND LINT_NVIM_SOURCES ${NVIM_SOURCES} ${NVIM_HEADERS})
 
 foreach(sfile ${NVIM_SOURCES})
   get_filename_component(f ${sfile} NAME)
-  if(${f} MATCHES "^(regexp_nfa.c)$")
-    list(APPEND to_remove ${sfile})
-  endif()
-  if(${f} MATCHES "^(regexp_bt.c)$")
-    list(APPEND to_remove ${sfile})
-  endif()
   if(WIN32 AND ${f} MATCHES "^(pty_process_unix.c)$")
     list(APPEND to_remove ${sfile})
   endif()
@@ -456,8 +450,6 @@ set(LUA_GEN_DEPS ${GENERATOR_PRELOAD} $<TARGET_FILE:nlua0>)
 # NVIM_GENERATED_SOURCES: generated source files
 # These lists must be mutually exclusive.
 foreach(sfile ${NVIM_SOURCES}
-              "${CMAKE_CURRENT_LIST_DIR}/regexp_bt.c"
-              "${CMAKE_CURRENT_LIST_DIR}/regexp_nfa.c"
               ${GENERATED_API_DISPATCH}
               "${GENERATED_UI_EVENTS_CALL}"
               "${GENERATED_UI_EVENTS_REMOTE}"

src/nvim/regexp.h

@@ -17,12 +17,8 @@
 #define REX_USE        2       ///< to allow \z\1 et al.
 #define REX_ALL       (REX_SET | REX_USE)
 
-// regexp.c
-// uncrustify:off
 #ifdef INCLUDE_GENERATED_DECLARATIONS
 # include "regexp.h.generated.h"
-# include "regexp_bt.h.generated.h"
 #endif
-// uncrustify:on
 
 #endif  // NVIM_REGEXP_H