fix(VFileInput): unindent input when icon is empty

[jacekkarczmarczyk]

Description

also removes tab index from icon, it allowed to tab the icon but enter/space didn't do anything, without it it's still clickable

Motivation and Context

fixes #8049

How Has This Been Tested?

playground, unit

Markup:

<template>
  <v-container>
    <v-file-input prepend-icon="" />
    <v-file-input />
    <v-file-input prepend-icon="mdi-home" />
  </v-container>
</template>

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Improvement/refactoring (non-breaking change that doesn't add any features but makes things better)

Checklist:

• The PR title is no longer than 64 characters.
• The PR is submitted to the correct branch (master for bug fixes and documentation updates, dev for new features and breaking changes).
• My code follows the code style of this project.
• I've added relevant changes to the documentation (applies to new features and breaking changes in core library)
• I've added new examples to the kitchen (applies to new features and breaking changes in core library)

[codecov]

Codecov Report

Merging #8078 into master will increase coverage by 0.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #8078      +/-   ##
==========================================
+ Coverage   85.75%   85.76%   +0.01%     
==========================================
  Files         334      334              
  Lines        9090     9090              
  Branches     2412     2413       +1     
==========================================
+ Hits         7795     7796       +1     
+ Misses       1207     1206       -1     
  Partials       88       88

Impacted Files	Coverage Δ
...es/vuetify/src/components/VFileInput/VFileInput.ts	82.81% <100%> (ø)	⬆️
packages/vuetify/src/components/VSelect/VSelect.ts	94.13% <0%> (+0.36%)	⬆️

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