Fix (mvThemes.cpp): Add missing ImGuiStyleVar_TabBarOverlineSize

[nvglucifer]

---

name: Pull Request
about: Create a pull request to help us improve
title: 'Fix (mvThemes.cpp): Add missing ImGuiStyleVar_TabBarOverlineSize'
assignees: @hoffstadt

---

Description:
Add missing ImGuiStyleVar_TabBarOverlineSize (only for ImGuiStyleVar_TableAngledHeadersAngle to work).

fixing an issue about: TableAngledHeaderAngle does not work outside of Style Editor (https://discord.com/channels/736279277242417272/1424799834006884483)

Concerning Areas:
I was tinkering with TabBarOverlineSize in some other places (mvPyUtils.cpp, dearpygui.cpp), but it seem only work on docked windows, also seem imgui 1.91.8 improved it (DPG using 1.91.0).
So, this PR only for ImGuiStyleVar_TableAngledHeadersAngle to work.

[v-ein]

BTW this issue also affects several other styles. Here are all the styles that don't work in 2.0/2.1:

TableAngledHeadersAngle
SelectableTextAlign
SeparatorTextBorderSize
SeparatorTextPadding
DockingSeparatorSize

[v-ein]

Looks good!

[v-ein]

Here's the test script I've come up with.

import dearpygui.dearpygui as dpg

dpg.create_context()
dpg.configure_app(docking=True)
dpg.create_viewport(title=f"Test - {dpg.get_dearpygui_version()}", width=500, height=400)

with dpg.theme() as theme:
    with dpg.theme_component():
        dpg.add_theme_style(dpg.mvStyleVar_SelectableTextAlign, 1, 0.5)
        dpg.add_theme_style(dpg.mvStyleVar_SeparatorTextPadding, 4, 20)
        dpg.add_theme_style(dpg.mvStyleVar_SeparatorTextBorderSize, 8)
        # This one isn't going to work anyway, see #2312
        dpg.add_theme_style(dpg.mvStyleVar_DockingSeparatorSize, 16)

dpg.bind_theme(theme)
with dpg.window(label="Dock here", width=500, height=500):
    # dpg.bind_item_theme(dpg.last_item(), theme)
    dpg.add_selectable(label="Lorem ipsum", width=150)
    dpg.add_separator(label="dolor sit")
    dpg.add_text("amet")


with dpg.window(label="Dock me", width=300, height=150):
    dpg.add_text("Dock me onto the other window\nto see the docking separator.")

dpg.setup_dearpygui()
dpg.show_viewport()
# In the correctly working version of DPG, styles listed in `theme` will be applied
# to the GUI right away, and any changes to them in the style editor will not affect
# anything.
dpg.show_style_editor()
# Some styles are only present in Dear ImGui's style editor, not in DearPyGui's one.
dpg.show_imgui_demo()
dpg.start_dearpygui()
dpg.destroy_context()