Grid theme applies generic input element selectors inside grid, causing unintended styling side effects

[georgianastasov]

Description

After updating from:

• @infragistics/igniteui-angular 20.1.9 + igniteui-theming 22.1.0
  to:
• @infragistics/igniteui-angular 21.0.4 + igniteui-theming 24.0.2

the theme adds selectors that style all native <input> elements inside the grid:

.igx-grid__td input,
.igx-grid-thead__title input,
.igx-grid-th input {
  margin: 0 auto;
  max-width: 100%;
}

This unintentionally affects user-provided inputs in cell/header templates (alignment/width changes). The requested fix is to avoid generic element selectors and scope styling to grid-owned inputs only (e.g., via a class).

Reproduction

1. Use @infragistics/igniteui-angular@21.0.4 + igniteui-theming@24.0.2.
2. Render an igx-grid with a cell or header template containing a native <input>.
3. Observe input gets margin: 0 auto and max-width: 100% and appears misaligned vs older versions.

Repro: https://stackblitz.com/edit/xh2uktr3?file=src%2Fapp%2Fgrid%2Fgrid-column-hiding-toolbar-sample%2Fgrid-column-hiding-toolbar-sample.component.html

Acceptance Criteria

• Remove/refactor grid theme rules that target input by element selector inside the grid.
• Scope styling to Ignite UI grid-owned inputs only (internal class/structure).
• Custom/user template inputs inside the grid are not affected by default.