This splits up interface_templates.c (currently 8463 lines) into multiple files.

• interface_template_color_picker.c
• interface_template_color_ramp.c
• interface_template_curve.c
• interface_template_id.c
• interface_template_layers.c
• interface_template_list.c
• interface_template_jobs.c
• interface_template_operator_props.c
• interface_template_preview.c
• interface_template_search_common.c
• interface_template_search_menu.c
• interface_template_search_operator.c

interface_templates.c has been kept for smaller templates,
also kept modifiers since there is work on a branch that changes this area.

Main down side of this patch is that it splits logic across interface_template_id.c and interface_template_search_common.c which makes me not so keen to commit this.

• ui_template_common_search_menu
• ui_template_common_search_menu_add_button
• UI_rna_update_cb
• ui_search_has_word_prefix

These functions have been added to interface_intern.h.

Alternative approaches could be:

• Keep interface_template_id.c & interface_template_search_common.c in interface_templates.c.
• Move every template function into it's own file (even small functions), add a shared interface_templates_intern.h header - possibly in their own directory.