[InputMethodNames] Update strings description and meaning

Update according to description in http://go/cros-input-methods-naming.
Also update Bangali to Bangla and Myanmar to Burmese/Myanmar

Bug: 889763
Change-Id: I53bf124a52c8064e3ab11d2b1a3b022559b7ba06
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2551897
Commit-Queue: My Nguyen <myy@chromium.org>
Reviewed-by: Darren Shen <shend@chromium.org>
Cr-Commit-Position: refs/heads/master@{#830089}

ui/chromeos/ui_chromeos_strings_grd/IDS_IME_NAME_KEYBOARD_BENGALI_PHONETIC.png.sha1

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ui/chromeos/ui_chromeos_strings_grd/IDS_IME_NAME_KEYBOARD_MYANMAR.png.sha1

+47fa07a0829bbd576e723e3919f2978a1efba2fd
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ui/chromeos/ui_chromeos_strings_grd/IDS_IME_NAME_KEYBOARD_MYANMAR_MYANSAN.png.sha1

+47fa07a0829bbd576e723e3919f2978a1efba2fd
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ui/chromeos/ui_chromeos_strings_grd/IDS_IME_NAME_TRANSLITERATION_AM.png.sha1

+5d5ec898f24a116e7733dad36bfc901d885ab0df
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ui/chromeos/ui_chromeos_strings_grd/IDS_IME_NAME_TRANSLITERATION_BN.png.sha1

+fa1efd1691850c4f1c924baa4a769f3eb65ee647
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