feat(gitsign): improve gitsign inline add and delete colors

[AndreasNasman]

This PR aims to improve the colors of changed text when running :Gitsigns preview_hunk with transparent_background = false (see the screenshot below).

For the dark themes, the cursor color seems to "conflict" with the diff colors, making it hard to track the cursor if focusing a hunk and, e.g., copying some text.

For GitSignsAddInline, it took the color of

nvim/lua/catppuccin/groups/syntax.lua

Line 73 in faf15ab

DiffAdd = { bg = U.darken(C.green, 0.18, C.base) }, -- diff mode: Added line |diff.txt|

and doubled the amount from 18 to 36. I did the same with GitSignsDeleteInline and

nvim/lua/catppuccin/groups/syntax.lua

Line 75 in faf15ab

DiffDelete = { bg = U.darken(C.red, 0.18, C.base) }, -- diff mode: Deleted line |diff.txt|

Latte

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Frappe

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Macchiato

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Mocha

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[AndreasNasman]

I'm unsure if I should add some O.transparent_background checks. Since

nvim/lua/catppuccin/groups/integrations/gitsigns.lua

Line 8 in faf15ab

if O.transparent_background then

already does an outer check for the truthiness of O.transparent_background, I don't follow why the inner checks like

nvim/lua/catppuccin/groups/integrations/gitsigns.lua

Line 47 in faf15ab

GitSignsAddPreview = O.transparent_background and { fg = C.green, bg = C.none } or { link = "DiffAdd" },

are needed.

[vollowx]

I'm unsure if I should add some O.transparent_background checks. Since

nvim/lua/catppuccin/groups/integrations/gitsigns.lua

Line 8 in faf15ab

if O.transparent_background then

already does an outer check for the truthiness of O.transparent_background, I don't follow why the inner checks like

nvim/lua/catppuccin/groups/integrations/gitsigns.lua

Line 47 in faf15ab

GitSignsAddPreview = O.transparent_background and { fg = C.green, bg = C.none } or { link = "DiffAdd" },

are needed.

That makes sense, we could fix this in another PR.